Tiger Rattlesnake Ecology and Management
(Heritage Grant Number U97015 - Urban Rattlesnakes: A Management Plan)
FINAL REPORT
November 4, 2002
Matthew J. Goode and Michael D. Wall
School of Renewable Natural Resources
University of Arizona
Tucson, AZ 85721
Submitted to the Arizona Game and Fish Department
Heritage Urban Wildlife Program
Recommended Citation
Goode, M.J. and M.D. Wall. 2002. Tiger rattlesnake ecology and management.
Nongame and Endangered Wildlife Program Heritage Report. Arizona Game and Fish
Department, Phoenix, Arizona.
Disclaimer
The findings, opinions, and recommendations in this report are those of the investigators
who have received partial or full funding from Arizona Game and Fish Department
Heritage Fund. The findings, opinions, and recommendations do not necessarily reflect
those of the Arizona Game and Fish Commission of the Department, or necessarily
represent official Department policy or management practice. For further information,
please contact the Arizona Game and Fish Department.
Tiger Rattlesnake Ecology and Management – Goode & Wall i
Table of Contents
INTRODUCTION ...............................................................................................................1
METHODS.........................................................................................................................2
Study Area ...............................................................................................................2
Search Effort ............................................................................................................4
Road Cruising ..........................................................................................................4
Capture, Marking, Handling ....................................................................................4
Morphology..............................................................................................................5
Demography.............................................................................................................5
Reproduction............................................................................................................6
Radio Telemetry.......................................................................................................6
Spatial Ecology ........................................................................................................7
Growth .....................................................................................................................7
Feeding and Diet ......................................................................................................8
Habitat Analyses ......................................................................................................8
Small Mammal Trapping .........................................................................................9
Lizard Abundance Index........................................................................................10
Amphibian and Reptile Observations ....................................................................10
Data Analyses ........................................................................................................10
RESULTS AND DISCUSSION........................................................................................10
Search Effort ..........................................................................................................10
Road Cruising ........................................................................................................11
Tiger Rattlesnake Ecology and Management – Goode & Wall ii
Capture-Recapture .................................................................................................14
Demography...........................................................................................................15
Morphology............................................................................................................17
Reproduction..........................................................................................................19
Growth ...................................................................................................................26
Spatial Ecology ......................................................................................................29
Feeding and Diet ....................................................................................................31
Habitat....................................................................................................................37
Small Mammal Trapping .......................................................................................40
Lizard Abundance Index........................................................................................41
MANAGEMENT IMPLICATIONS .................................................................................43
A MANAGEMENT PLAN FOR URBAN RATTLESNAKES........................................47
Direct Killing of “Nuisance” Rattlesnakes ............................................................47
Translocation of “Nuisance” Rattlesnakes.............................................................48
Residential Development.......................................................................................50
Golf Course/Resort Development..........................................................................51
Road Mortality.......................................................................................................52
Rattlesnake – Pet Encounters.................................................................................53
ACKNOWLEDGEMENTS...............................................................................................53
LITERATURE CITED......................................................................................................54
APPENDIX A....................................................................................................................57
Tiger Rattlesnake Ecology and Management – Goode & Wall iii
Tables
1. Tiger rattlesnakes captured per unit effort ...................................................................11
2. Tiger rattlesnakes encountered while road cruising.....................................................12
3. Amphibian and reptile species observed while road cruising......................................12
4. Tiger rattlesnake morphometric data ...........................................................................18
5. Tiger rattlesnake body and head size data ...................................................................19
6. Date ranges of tiger rattlesnake reproductive activity .................................................21
7. Average litter size of Arizona rattlesnakes ..................................................................23
8. Morphological data for tiger rattlesnake litter .............................................................24
9. Mean SVL of gravid tiger rattlesnakes ........................................................................24
10. Summary of tiger rattlesnake movement and home range data...................................32
11. Relative abundance, by site, of lizards.........................................................................36
12. Tiger rattlesnake microhabitat data..............................................................................38
13. Small mammals trapped at Tanque Verde Ridge ........................................................40
14. Incidental reptiles and amphibians encountered ..........................................................41
15. Relative abundance of prey lizards by season .............................................................42
16. Relative abundance of prey lizards by habitat type .....................................................43
Tiger Rattlesnake Ecology and Management – Goode & Wall iv
Figures
1. Photograph of adult male tiger rattlesnake ....................................................................2
2. Map of Saguaro National Park and surrounding urban areas ........................................3
3. Aerial photograph of tiger rattlesnakes encountered while road cruising ...................13
4. Tiger rattlesnakes by site .............................................................................................14
5. Sex by site ....................................................................................................................15
6. Age class by site...........................................................................................................16
7. Size class distribution ..................................................................................................16
8. Adult size by site..........................................................................................................20
9. Ratio of tail length to SVL by sex ...............................................................................20
10. Semen present by season .............................................................................................21
11. Reproductive activity by year ......................................................................................22
12. Proportion giving birth.................................................................................................23
13. Rainfall by season and year .........................................................................................26
14. Growth by season.........................................................................................................27
15. Growth by year ............................................................................................................27
16. Growth per year of radio and non-radioed snakes .......................................................28
17. Aerial photograph of all tiger rattlesnake locations.....................................................29
18. Minimum convex polygon home ranges for selected tiger rattlesnakes......................30
19. Minimum convex polygon home range by season ......................................................33
20. Minimum convex polygon home range by gender ......................................................34
21. Tiger rattlesnake diet....................................................................................................35
Tiger Rattlesnake Ecology and Management – Goode & Wall v
22. Percent bolus by season ...............................................................................................35
23. Diet by sex ...................................................................................................................36
24. Diet by site ...................................................................................................................37
25. Seasonal variation in habitat selection.........................................................................39
26. Aerial photograph of transboundary movements at Tanque Verde Ridge ..................44
27. Aerial photograph of transboundary movements at Rocking K ..................................45
Tiger Rattlesnake Ecology and Management – Goode & Wall 1
INTRODUCTION
Prior to this study, the tiger rattlesnake (Crotalus tigris) was one of the least studied
rattlesnake species in the United States (Ernst 1992). Much of what was known about
tiger rattlesnakes came from a small number of field observations and museum
specimens, consisting mainly of physical descriptions, scale counts and information on
their distribution (Baird 1859, Amaral 1929, Klauber 1931, Gloyd 1940, Campbell &
LaMar 1989). Knowledge of the natural history of this secretive species was largely
anecdotal (Gloyd 1937, Fowlie 1965, Klauber 1972; Armstrong & Murphy 1979; Lowe,
et al. 1986). Basic ecological and physiological data were virtually nonexistent until
Beck (1995) published data on a small sample (n = 3) of male tiger rattlesnakes that he
studied using radiotelemetry.
Duvall et al. (1995) tracked 6 tiger rattlesnakes using radiotelemetry, but their objective
was to document the presence of rattlesnakes in isolated preserves throughout the
Phoenix, Arizona metropolitan area, and to assess the degree to which these snakes were
using surrounding urbanized areas. Because they only located radio-equipped snakes a
total of 32 times, they learned a limited amount about tiger rattlesnake biology.
However, they recognized the need for a more detailed study of rattlesnakes living near
urbanized areas. In this vein, McNally & Hare (1996) radiotracked several rattlesnakes,
one of which was a male tiger rattlesnake, to determine movement patterns of
rattlesnakes that were translocated by the Rural Metro Fire Department (RMFD) in
Tucson. These snakes appeared to exhibit aberrant movement patterns, and little was
learned about the natural behavior of tiger rattlesnakes.
Herpetologists have recognized the need for a detailed study of C. tigris for decades
(Gloyd 1940, Klauber 1956, Ernst 1992, Rubio 1998). Therefore, our goal was to expand
our knowledge of tiger rattlesnakes by intensively studying a large sample of radiotagged
snakes. In this report we present the results of the first five years (1997 – 2001) of an
ongoing, long-term study of tiger rattlesnakes at an urban/wildland interface near Tucson,
Arizona. Specifically, we studied tiger rattlesnakes at Saguaro National Park (SNP), and
at two sites on private land immediately adjacent to the park: a low-density residential
area, and the future site of a large urban development. We also obtained information
from tiger rattlesnakes captured by RMFD personnel.
In addition to studying tiger rattlesnake natural history and ecology, our objective was to
use this knowledge to develop more effective management strategies for rattlesnakes in
general. In particular, there is a need to manage rattlesnakes that live along the
boundaries of parks and preserves and that move into adjacent urbanized areas. Tiger
rattlesnakes are a good choice for investigating the effects of urbanization on rattlesnakes
for several reasons. The range of the tiger rattlesnake in Arizona is centered around
Phoenix and Tucson, two rapidly expanding urban areas surrounded by wildlands. Tiger
rattlesnakes prefer rocky desert uplands; these upland areas are also considered prime real
estate, and they are being developed at an alarming rate. An estimated 3,000-5,000
Tiger Rattlesnake Ecology and Management – Goode & Wall 2
rattlesnakes, including tiger rattlesnakes, are removed by RMFD every year from the
yards of residents living in Tucson (McNally 1995, G. Good, RMFD, pers. comm.). In
Phoenix, rattlesnake removal services are also provided by the fire department and by
members of the Arizona Herpetological Association, an amphibian and reptile
enthusiasts’ club (J. Feldner, pers. comm.). Rattlesnake management is also an issue at
SNP. One of the biggest concerns facing the park is what to do about wildlife that move
in and out of the park, especially as the city of Tucson continues to expand, further
surrounding the park (Goode 2001, SNP Resource Management Plan). This is also true
for other urban/wildland interfaces in the Tucson and Phoenix areas, including US Forest
Service lands in the Santa Catalina and Rincon Mountains, Pima County Park lands in the
Tucson and Tortolita Mountains, municipal lands comprising the Phoenix mountain
parks, and a variety of other land ownership entities throughout Pima and Maricopa
counties. Our goal was to use the results of this research to address these growth-related
concerns.
METHODS
Study Area
We studied tiger rattlesnakes (Figure 1) at three sites in the Rincon Mountain District of
SNP (Figure 2). The Tanque Verde Ridge (TVR) site is located in the extreme southwest
Figure 1. Adult male tiger rattlesnake (Crotalus tigris). Photograph by Chris Scott.
Tiger Rattlesnake Ecology and Management – Goode & Wall 3
corner of the park. This site is bordered by Old Spanish Trail, a busy commuter road that
runs along the west boundary of the park, and a low-density housing area immediately
adjacent to the south boundary. The Rocking K (RK) site is situated along the park’s
south boundary approximately 4 km east of TVR. This area is the future site of the
Rocking K development, a large scale project consisting of a resort and golf courses,
approximately 5,000 dwelling units, and small commercial zones. The Loop Road (LR),
the only road in the park used by visitors, begins and ends at the Visitor Center and it alos
provides access to the Javelina Picnic Grounds.
Figure 2. Map of Saguaro National Park and surrounding urban areas, showing all three
study areas. LR = Loop Road; TVR = Tanque Verde Ridge; RK = Rocking K Ranch.
Figure 2. Map of Saguaro National Park and surrounding urban areas, showing all three
study areas. LR = Loop Road; TVR = Tanque Verde Ridge; RK = Rocking K Ranch.
All three sites are characterized by steep rocky slopes, ridges with exposed bedrock, and
bajadas dissected by numerous washes, some of which are characterized by relatively
well developed soil terraces and xeroriparian vegetation. Vegetation is typical of
Sonoran Desertscrub, Arizona Upland Subdivision (Turner & Brown 1982). Common
plants include saguaro (Carnegia gigantea), foothill paloverde (Cercidium
microphyllum), brittlebush (Encelia farinosa), prickly pear and cholla (Opuntia spp.), and
velvet mesquite (Prosopis velutina). Elevation at all three sites ranges from
approximately 900 – 1100 m (2,940 – 3,700 ft). We also obtained information from tiger
rattlesnakes, which were removed from residences by RMFD personnel. These snakes
originated from throughout the foothills of the Santa Catalina Mountains, approximately
10-25 km northwest of our main study areas at SNP.
LR
TVR
RK
KK
Tiger Rattlesnake Ecology and Management – Goode & Wall 4
Search Effort
When we began the study in August 1997, with the aid of numerous volunteers, we
conducted walking searches in an attempt to obtain tiger rattlesnakes for radiotelemeter
implants. In 1998, we turned our attention to radiotracking the snakes we captured and
implanted in 1997. We continued to conduct a limited number of searches in 1998,
acquiring several more snakes for implantation. In 1999, we began studying tiger
rattlesnakes at RK, where we conducted several searches in an attempt to acquire snakes
for implantation. In 2000, we did not conduct any walking searches specifically for tiger
rattlesnakes; however, we obtained numerous snakes from tortoise researchers who
captured them while conducting distance sampling at RK. In 2001, we conducted one
walking search at TVR, and we received several more snakes from tortoise researchers
who were continuing to conduct distance sampling at RK.
We also acquired snakes while radiotracking, including those found in association with
our radiotagged snakes, which occurred on several occasions during the mating season.
Because the amount of time searching for snakes while radiotracking is less than when
conducting snake hunts, we compared the number of snakes captured during each activity
to arrive at an estimate of total search effort. We estimated search effort of tortoise
researchers to be equal to search effort while conducting snake hunts, because it is likely
that tortoise researchers missed few tiger rattlesnakes while searching (D. Swann, R.
Averill-Murray, pers. comm.).
Road Cruising
We spent a significant amount of time road cruising the LR, where we acquired numerous
snakes. The LR is nine miles in length, winding through relatively pristine desert. The
LR begins at approximately 1000 m, and reaches a maximum elevation of approximately
1200 m. We found tiger rattlesnakes along a 3.7 mile stretch of the LR, where the road
winds through rocky foothill areas on the west side of Tanque Verde Ridge. We did not
encounter any tiger rattlesnakes in lower elevation creosote flats.
Capture, Marking and Handling
We captured snakes using 24” tongs (Whitney, Inc). We transported snakes in cloth bags
to the senior author’s residence for processing (e.g., measured, sexed, palpated). We
permanently marked each snake by injecting a passive integrated transponder (PIT tag)
under the skin. These tiny electronic devices are about the size of a grain of rice. PIT
tags enabled us to identify individuals by passing a PIT tag reader (Destron-Fearing Co.),
which displays a 10-digit alphanumeric code, over the snake’s body. We coded digits 0-9
with different paint colors, which were then used to paint the first three proximal rattle
segments of the rattle based on the last three numeric digits of the alphanumeric code.
This gave each snake a unique rattle paint code, making it unnecessary to recapture
snakes observed in the field if the paint colors were visible. In some cases, when snakes
Tiger Rattlesnake Ecology and Management – Goode & Wall 5
were recaptured for growth measurements or to replace their radiotelemeter, we repainted
the rattle if necessary. In general, paint marks were quite resilient; however, over time
they will either wear off or the rattle segments containing the paint mark will break off.
Therefore, they are not considered permanent. The paint mark also allowed us to
quantify the number of times a rattlesnake shed its skin.
We used plastic tubes (JB Specialties, Inc.), a hook (Rattlesnake Museum, Albequerque,
NM) and a “squeezebox” (a wooden box lined with foam padding) to safely handle
rattlesnakes during capture and processing. Our experience handling venomous snakes
minimized risk to both the snakes and ourselves. Snakes were released within 3-48
hours, depending on whether or not they were chosen for a radiotelemeter implant.
Morphology
We recorded snout-vent length (SVL), tail length, mass, head width and head length for
all snakes captured. We measured SVL using a squeezebox. We traced the total length
of the snake (minus the rattle) twice on the plexiglass cover of the squeezebox. We
measured the trace twice to help insure accuracy. If measurements differed by greater
than 1% of the total length, then we measured again until we obtained two measurements
that were within 1% of each other. We also traced the outline of the head to get length
and width measurements.
We tubed snakes in order to measure tail length, which we subtracted from the total
length to arrive at SVL. We weighed snakes in a cloth bag and then subtracted the mass
of the empty bag to determine the mass of the snake. We calculated the mass of the
snake per unit body length by dividing the mass by SVL. This produces a body condition
index (BCI), which can be compared among individuals. We also calculated the ratio of
tail length to body length to facilitate sexing, as female tails are shorter than males’
relative to their body length.
Demography
We sexed all snakes captured and classified each one into one of three age classes: adult,
subadult, and neonate. For a female snake to be classified as an adult, it had to exceed
the minimum size at which we found gravid individuals. For a male snake to classified
as an adult, it had to exceed the minimum size at which males have been found to be
reproductively mature (Goldberg 1999). We distinguished neonates from subadults
based on their small size and by the presence of a rattle consisting of only one segment
called the button, indicating that the snake had only shed once, approximately one week
after birth.
Tiger Rattlesnake Ecology and Management – Goode & Wall 6
Reproduction
Each time we tracked a snake, we recorded whether or not it was with a conspecific of
the opposite sex. We classified each conspecific pairing into one of three categories:
accompaniment, courtship, or copulation. We defined accompaniment as a male and
female located within 1 m of each other. Courtship consisted of obvious behaviors such
as chin-pressing and tail-searching (Klauber 1972). Copulation, which can be difficult to
discern from courtship (Schuett & Gillingham 1988), was only scored if we were certain
that intromission had occurred, as evidenced by a distended cloaca of the female, or the
female dragging the male around while in a copulatory lock.
We palpated female snakes to assess reproductive condition. Small, hard ovarian
follicles were easily palpated on females in the late summer and fall. Larger, softer
yolking follicles were evident in spring, and embryos could be detected in summer.
Although experience has enabled us to be fairly accurate in our assessment of female
reproductive condition, there is some margin for error, especially in determining the exact
number of ova or embryos.
Although we tracked several radiotagged females, which undoubtedly gave birth, we
were unable to obtain any data on their litters because we were unsuccessful in finding
the neonates. On several occasions, we had females, which were obviously gravid, make
movements after a long period of quiessence. Upon locating the female, it was obvious
she had given birth, however, we were unable to find her offspring when we returned to
her previous location.
In an attempt to assess male reproductive condition, we recorded the presence of semen
expressed from the hemipenal shafts. We have not yet determined if semen contains live
sperm; however, a reptile and amphibian veterinarian (J. Jarchow, pers. comm.) indicated
that live sperm are almost certainly present in the semen of mature males during the
mating season.
Radiotelemetry
We surgically implanted temperature-sensing radiotelemeters (Holohil, Ltd., Model SR2)
into 35 tiger rattlesnakes. Radiotelemeters were designed to last two years;
unfortunately, more than half failed prematurely due to faulty batteries. Therefore, we
were unable to track the snakes we captured in 1997-1998 as long as originally intended.
In a few cases, individuals were only tracked a few times before their radiotelemeter
failed. Despite these problems, we were still able to follow several individuals for
multiple years, and we were able to obtain a large dataset on numerous individuals.
We only implanted snakes if the mass of the radiotelemeter (11.6 g) was 5% or less of the
snake’s mass. This resulted in a minimum mass of 232 g to be eligible for an implant,
although a snake also had to be large enough in diameter (determined by visual
Tiger Rattlesnake Ecology and Management – Goode & Wall 7
inspection and based on experience) to receive an implant. Occasionally, a snake met the
minimum mass criteria but was rejected because it appeared to be too thin or unhealthy.
We anesthetized snakes using Isoflurane (Abbott Laboratories), an inhalant, which is
highly soluble in tissue and allows for precise dosing. Using a sterile procedure
(modified from Reinert & Cundall 1982), we implanted transmitters into the peritoneum
(i.e., gut cavity), with the antennae placed under the skin and stretched toward the head to
increase the range of signal detection. Several snakes received multiple implants. No
snakes died or showed any obvious ill effects of implantation.
Spatial Ecology
We used either a Trimble (Trimble, Inc.) or Garmin E-Map (Garmin, Inc.) global
positioning system (GPS) receiver to record snake locations. We post-processed
locations recorded with the Trimble receiver using Pathfinder software (Trimble, Inc.) to
obtain 1-3 m accuracy. We used base station files obtained from the US Forest Service
office at Tucson, which was approximately 15 miles from our study area, for differential
correction. Locations recorded with the Garmin receiver were not post-processed.
However, these locations were accurate to within 4-7 m because they were obtained after
GPS signals were no longer being scrambled by the government. All GPS data were
imported into ArcView (ESRI, Inc.) for
display and spatial analyses using the Animal Movement Analysis extension (obtained
online from Alaska Biological Science Center, USGS-Biological Resources Division).
We used a variety of parameters to characterize tiger rattlesnake movement patterns,
including total distance moved, mean distance moved per day, mean distance moved per
movement bout, maximum distance moved, and whether or not the snake was moving
when located. To characterize home ranges, we estimated their size using the minimum
convex polygon (MCP) technique and the 95% active kernal technique. We estimated
core activity areas using the 50% isopleth generated by the active kernal technique. This
area contains half of all the locations for a given snake. We examined annual and
seasonal differences in movement patterns and home range size and use when sample
sizes permitted.
Growth
We used morphological data and information on shedding frequency to examine growth.
We attempted to recapture radiotagged snakes upon emergence from winter dens in the
spring and again before they reentered their dens in the fall in order to remeasure them.
By catching snakes just before and just after they overwintered, we were able to examine
growth rates during the active season and determine the effects of hibernation on growth
and mass. We also compared the growth of radiotelemetered snakes with data from non-radiotelemetered
snakes, which were recaptured opportunistically. By comparing
radiotelemetered snakes with non-radiotelemetered snakes, we were able to indirectly
examine the effects, if any, that implants may be having on snakes.
Tiger Rattlesnake Ecology and Management – Goode & Wall 8
Feeding and Diet
We obained information on tiger rattlesnake diet through analyses of fecal matter, which
we obtained by forcing feces out of the hind gut. Fecal samples were frozen and later
placed in water to thaw and to dissolve feces into identifiable prey remains. Prey remains
consisted of hair, claws, bones, teeth, feathers and scales. We were able to identify prey
remains to class level in all cases, genus level in some cases, and species level in a few
cases. We have recently begun more extensive analyses of prey remains in an attempt to
refine our ability to identify remains to the species level. This requires microscopic
analyses of mammal hair, and time-consuming comparisons of minute bone fragments
and teeth with museum reference collections, which in some cases, have yet to be
prepared.
We also palpated all captured and recaptured snakes to determine if we could detect a
food bolus, indicating recent feeding. Because snakes swallow their food whole, it is
often possible to determine if they have fed recently by the presence of a large bulge or
bolus in the stomach or fore gut. However, due to the strength of their axial muscles, and
the action of their digestive enzymes, a snake could have eaten recently, but an obvious
bolus may not be detectable. Via palpation, it is often possible to feel the prey item in the
gastrointestinal tract. However, in most cases, it is difficult to unambiguously define
prey items. Therefore, we only included prey items if we were absolutely certain they
were present.
We kept detailed records of several feeding episodes, which we observed under natural
conditions throughout the course of the study. Although we did not observe feeding
often enough to have any statistical significance, the episodes we observed provide us
with valuable information on the natural history of tiger rattlesnakes.
Habitat Analyses
We examined microhabitat and macrohabitat use. For microhabitat analyses, in 1997 we
recorded data on several variables within a 1-m2 area centered around each snake
location. We waited until radiotelemetered rattlesnakes moved to another location before
collecting microhabitat data to avoid disturbing the snakes. We gathered data at random
sites throughout each snake home range, which allowed us to compare microhabitat use
versus availability using logistic regression analysis, which allowed us to make
inferences about the preferred habitat of tiger rattlesnakes. Within each 1-m2 quadrat, we
recorded the percentage of exposed ground, litter, grass, forb, shrub, tree, cactus, and
total canopy cover. We recorded whether or not a woodrat midden was present, and the
distance to the nearest midden if one was not present. We recorded data on geomorphic
substrate type, which was based on particle size and fell into seven categories: bedrock,
boulder, rock, gravel, pebble, sand, and soil. We recorded the dominant species of grass,
forb, shrub, tree, and cactus. And, we recorded the slope and aspect of each snake
location.
Tiger Rattlesnake Ecology and Management – Goode & Wall 9
To compare macrohabitat use versus availability, we created a georeferenced map of the
TVR study site based on tiger rattlesnake habitat types. Habitat types were based on our
observations of tiger rattlesnake movement patterns. We identified four habitat types:
exposed rock outcrops on ridges, rocky slopes, disected bajada, and xeroriparian wash
consisting of the terrace with soil development, and the sandy active channel. We created
the habitat map by walking the perimeter of each habitat type using a Trimble GPS unit.
We generated line data, which were differentially corrected using carrier phase post-processing,
to obtain 1-3 m accuracy. We analyzed habitat data by overlaying the habitat
map with home range polygons and calculating the proportion of habitat types used
compared to the proportion of habitat types available within each home range. At the
landscape scale, we compared the proportion of tiger rattlesnake habitat types available
within the entire study area with the proportion of habitat types within each home range.
To conduct this analysis, we defined the study area as a polygon containing all known
tiger rattlesnake locations.
Small-Mammal Trapping
We trapped nocturnal rodents in different habitat types and at randomly selected snake
locations at different times throughout the course of the study. Our objective was to
combine the results of small-mammal trapping with diet and fecal analyses to in an
attempt to gain greater insight into foraging ecology and diet of tiger rattlesnakes. In
1997, we set five 16-trap grids centered around snake locations in different habitat types,
which we ran for five nights (400 trap-nights). This pilot effort helped us determine
relative abundance and species diversity at the Tanque Verde Ridge site, and it confirmed
previous observations that small mammals occur in relatively low numbers in rocky
foothill areas of the Sonoran Desert (D. Swann, pers. obs.). In 1998, after studying tiger
rattlesnakes for one year and becoming more familiar with their habitat use, we set four
50-trap grids (with traps spaced at 5-meter intervals) in different habitat types: wash,
bajada, slope and ridge. We ran these grids for 8 nights for a total of 1600 trap-nights.
Where possible, when the number of individuals per species was six or greater, we used
Program CAPTURE to obtain abundance estimates. Unfortunately, capture-recapture
rates were very low in all habitat types, which led to wide confidence intervals, making it
difficult to draw meaningful conclusions.
To determine if small mammals might play a role in tiger rattlesnake movement patterns
at the microhabitat scale, we placed 9-trap grids centered around randomly chosen snake
locations. Each grid was paired with another grid, which was placed at a random
distance and direction from the grid at the snake location. The 9-trap array consisted of
three rows of three traps each with the center trap placed at the snake location (the snake
was no longer present at the location). Traps were spaced at 2-meter intervals. We
compared capture data from the grids at snake locations to the randomly placed grids.
We ran 20 grids (10 at snake locations and 10 at random locations) for four nights each
for a total of 720 trap nights. To examine small mammal species diversity by habitat
type, we pooled all trapping data.
Tiger Rattlesnake Ecology and Management – Goode & Wall 10
Lizard Abundance Index
We used data from our incidental lizard observations (see below) to develop an encounter
rate index of relative abundance and species diversity within different tiger rattlesnake
habitats. As with small-mammal trapping, our goal was to increase our understanding of
tiger rattlesnake foraging ecology and diet by characterizing the available prey base. We
recorded the habitat type (based on tiger rattlesnake habitat use) in which each lizard was
observed, providing us with both the diversity of lizard species and the relative
abundance within each species by habitat type and by season. We then compared this to
tiger rattlesnake habitat use to look for potential patterns.
Incidental Amphibian and Reptile Observations
We recorded all amphibians and reptiles observed while conducting tiger rattlesnake
research, whether radiotracking snakes, walking to and from our vehicles, or conducting
other activities such as small-mammal trapping and habitat measurements. Each time an
animal was observed we recorded the date, time, species, and habitat type. We also
recorded sex and age class if discernable. These data were used to examine relative
abundance of lizards, which was then compared to tiger rattlesnake movement patterns.
These data were also gathered to aid the park in current efforts to conduct a
comprehensive inventory of its herpetofauna.
Data Analyses
We used both graphical and statistical techniques to analyze data. We used ANOVA to
analyze morphological data. We used regression to analyze the relationship of tail length
to gender. We used t-tests to analyze differences in movement patterns and home range
size by sex and by season. We used logistic regression to analyze microhabitat data. All
data met assumptions for each statistical test. We considered tests to be statistically
significant at a£ 0.05.
RESULTS AND DISCUSSION
Search Effort
We recorded time spent conducting field activities (e.g., snake hunts, radiotracking) in
order to calculate the number of snakes captured per unit effort (Table 1). Road cruising
was by far the most efficient method, with an average of 4 person-hours required to
encounter a tiger rattlesnake. During dedicated snake hunts, we captured an average of
one tiger rattlesnake per 18 person-hours, which is more than four times the number of
hours needed to capture a snake while road cruising. Tortoise researchers only captured
an average of one tiger rattlesnake per 50 person-hours.
Tiger Rattlesnake Ecology and Management – Goode & Wall 11
Table 1. Number of tiger rattlesnakes captured per unit effort while conducting different
activities at three study areas (TVR = Tanque Verde Ridge, RK = Rocking K Ranch, LR =
Loop Road, μ = mean.)
Site Method Person-Hours Snakes Captured* Person-
Hours/Snake
TVR Snake Hunt
Radiotracking
212
761
12
31
18
25
RK Snake Hunts
Radiotracking
Tortoise Sampling
71
338
1168
4
39
22
18
9
53
LR Road Cruising 140 40 4
Totals 2690 148 μ = 18
*Includes recaptures
Snakes observed per unit effort may be used as an index of relative abundance, and as
such, may be useful for comparing across taxa. This type of encounter rate index may
have utility in a monitoring context, especially when reasonable estimates of absolute
abundance are difficult to obtain, which is usually the case for snakes. However, using
encounter rates as an index of relative abundance is likely to be confounded by a variety
of factors, including species differences in crypticity, habitat use, and activity patterns to
name a few. In any case, standardizing the number of snakes encountered by unit effort
seems necessary if any conclusions about relative abundance are to be drawn.
In comparison to other rattlesnake species, which we observed incidentally during this
study, tiger rattlesnakes appear to be more abundant. We observed 62 western diamond-backed
rattlesnakes during the study, which is an average of 42 person-hours per snake.
We observed only 5 black-tailed rattlesnakes, which is an average of one every 510
hours. Although these numbers would undoubtedly be greater if we were specifically
searching for these species, we feel that they are reflective of the relative abundance of
these rattlesnake species at our study areas.
Road Cruising
We captured a total of 40 tiger rattlesnakes (37 captures and 3 recaptures) on the LR,
(Figure 3; Table 1). We included 5 additional tiger rattlesnakes in our LR sample; 4 were
captured within 800 m of the road by biologists conducting research on tortoises in the
vicinity, and 1 was captured by us in Freeman Wash approximately 200 m from the road.
Tiger rattlesnakes encountered per unit effort varied from year to year (Table 2).
Tiger Rattlesnake Ecology and Management – Goode & Wall 12
Table 2. Summary of the number of tiger rattlesnakes encountered (including 3 recaptures)
on the Loop Road at Saguaro National Park from 1997-2001. The average number of hours
and miles driven required to encounter a tiger rattlesnake are given.
Year Snakes Encountered Hours/Snake Miles/Snake
1997 10 2.0 18.5
1998 16 1.4 16.9
1999 0 0 0
2000 4 11.6 124.3
2001 10 4.8 55.8
We documented 1478 individuals and 27 species of herpetofauna on the LR (Table 3).
The red-spotted toad (Bufo punctatus) was by far the most commonly observed species.
Table 3. Number of individuals of each amphibian and reptile species observed on the Loop
Road from 1997 – 2001. Total number of hours spent road cruising = 141; Total number of
miles driven = 1582.
Species No. Individuals Individuals/Hour Individuals/Mile
Bufo alvarius 340 2.41 0.215
Bufo cognatus 6 0.04 0.004
Bufo spp. 44 0.31 0.028
Bufo punctatus 601 4.26 0.380
Cnemidophorus tigris 2 0.01 0.001
Cophosaurs texanus 8 0.06 0.005
Coleonyx variegatus 130 0.92 0.082
Crotalus atrox 51 0.36 0.032
Crotalus molossus 5 0.04 0.003
Crotalus tigris 40 0.28 0.020
Heloderma suspectum 13 0.09 0.008
Hypsoglena torquata 17 0.12 0.011
Leptotyphlops humilis 1 0.01 0.001
Masticophis flagellum 3 0.02 0.002
Micruroides euryxanthus 1 0.01 0.001
Phrynosoma solare 16 0.11 0.010
Phylorhincus decurtatus 1 0.01 0.001
Pituophis catenifer 3 0.02 0.002
Rhinocheilus lecontei 11 0.08 0.007
Salvadora hexalepis 2 0.01 0.001
Sceloporus clarki 2 0.01 0.001
Scaphiophus couchi 48 0.34 0.030
Sceloporus magister 122 0.87 0.077
Tantilla hobartsmithi 1 0.01 0.001
Tiger Rattlesnake Ecology and Management – Goode & Wall 13
Table 3 (con’t.)
Species No. Individuals Individuals/Hour Individuals/Mile
Thamnophis cyrtopsis 1 0.01 0.001
Urosaurus ornatus 3 0.02 0.002
Uta stansburiana 1 0.01 0.001
Unidentified 14 0.10 0.004
Total 1487 10.54 0.931
The most commonly observed nocuturnal lizard was the banded gecko (Coleonyx
variagatus) and the most commonly observed diurnal lizard was the desert spiny lizard
(Sceloporus magister). The most commonly observed snake was the western diamond-backed
rattlesnake, followed closely by the tiger rattlesnake.
Figure 3. Aerial photograph showing the number of tiger rattlesnakes (n = 36) encountered
while conducting road cruising surveys on the Loop Road as Saguaro National Park. Tiger
rattlesnakes were captured only along a 3.7-mile segment where the road passes through
rocky foothills of the Rincon Mountains. No tiger rattlesnakes were encountered in lower
elevation creosote flats. Total number of hours spend road cruising = 141; total number of
miles driven = 1582.
Visitor
Center
Boundary
7.4 miles
3.7 miles
Creosote Flats
Rocky Foothills
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 14
Road cruising has been a popular method for sampling herpetofauna for decades (Klauber
1935). Due to the secretive nature of many species, it can be difficult to find animals in
numbers great enough to conduct meaningful analyses. This is one of the primary
reasons why herpetofauna have been poorly studied compared to more visible taxa such
as birds and mammals. Road cruising enables the researcher to cover a far greater area in
far less time, and it is generally repeatable over time. Problems associated with road
cruising include the nonrandom placement of roads, bias associated with the potential to
attract animals to warm pavement at night, and the effects of automobiles on the
abundance and behavior of some species.
Capture-Recapture
Not including recaptures, we captured and marked 169 tiger rattlesnakes from four sites
(Figure 4). We recaptured 21 snakes, excluding radio-equipped snakes, which we
periodically recaptured throughout the study to obtain data on growth. Due to low
recapture rates, we did not attempt to estimate population size or survival at any of our
sites.
Figure 4. Tiger rattlesnakes captured by site. TVR = Tanque Verde Ridge; RK = Rocking
K Ranch; LR = Loop Road; RMFD = Rural Metro Fire Department.
The number of tiger rattlesnakes obtained in this study was much higher than we
expected. Anecdotal information on tiger rattlesnakes led us to believe that they were
both rare (Wright & Wright 1957) and difficult to find (Lowe et al. 1986). Based on this
Tiger Rattlesnakes By Site
39
66
42
22
0
10
20
30
40
50
60
70
TVR RK LR RMFD
Site
No. Snakes
Tiger Rattlesnake Ecology and Management – Goode & Wall 15
study, it appears that tiger rattlesnakes can be locally abundant, especially in rocky
foothill areas. In fact, at our study area, tiger rattlesnakes are one of the most commonly
observed snakes.
The low of number of recaptures is probably not surprising based on prior research with
rattlesnakes. Many snake researchers have commented on the difficulty in estimating
population size and survival in snakes due to their secretive lifestyles. The actual
abundance of snakes is likely much greater than their apparent rarity would suggest.
However, given the large number of hours we spent in a relatively small area, it remains
an enigma as to why we have such a low number of recaptures. In any case, when
recapture rates are low, population and survival estimates based on capture-recapture
probabilities tend to have extremely large confidence intervals, thereby limiting their
value. In cooperation with SNP and Arizona Game and Fish Department personnel, we
are exploring the use of distance sampling for estimating tiger rattlesnake abundance.
Demography
Gender (Figure 5) and age-class structure (Figure 6) at all four sites (including RMFD
Sex by Site
0
10
20
30
40
50
TVR RK LR RMFD
Site
N
Males
Females
Figure 5. Sex ratios of all tiger rattlesnakes captured at all four sites from 1997-2001
snakes) were heavily biased towards adult males. Size class structure for all sites
combined reflects a bias towards larger snakes (Figure 7); however, males and females
did not differ in SVL at TV (t = 1.59, df = 36, p < 0.119).
Tiger Rattlesnake Ecology and Management – Goode & Wall 16
Age Class by Site
0
10
20
30
40
50
TVR RK LR RMFD
Site
N
Adults
Sub-Adults
Neonates
Figure 6. Age-classes of all tiger rattlesnakes captured at all four sites from 1997-2001.
Size Class Distribution
0
5
10
15
20
25
30
35
40
250-300
301-350
351-400
401-450
451-500
501-550
551-600
601-650
651-700
701-750
751-800
SVL (mm)
N
Males
Females
Figure 7. Size class distribution of all tiger rattlesnakes captured at all sites combined from
1997-2001.
Tiger Rattlesnake Ecology and Management – Goode & Wall 17
Many studies have documented a strong bias towards large adult male rattlesnakes
(Duvall et al. 1992). Speculation as to why males are easier to find than females
abounds. Males are larger and therefore more conspicuous, which probably makes them
easier to observe. A predominance of data on sex ratios in snakes points toward
equality,making it unlikely that there are more males present in the population. Males are
bigger risk takers, especially in a polygynous mating system where females are a scarce
resource. This is the case with most temperate pit vipers, as females tend to give birth
every 2-3 years meaning that a segment of the female population will be unreceptive in
any given year. This causes males to move even further in pursuit of females, thus
rendering them more likely to be observed.
We observed interesting interpopulational differences in age-class structure among our
study areas. During the first two years of the study, we did not observe a single subadult
tiger rattlesnake. After processing 70 adult snakes, we finally encountered a subadult at
TVR in late August of 1999. This subadult remains the only one we observed at TVR.
Similarly, we have only observed two subadults from the LR and we are yet to obtain a
subadult from RMFD snakes, although we did acquire one neonate from RMFD
personnel.
In contrast, we have encountered 16 subadults and three neonates from the RK
population. Considering how close it is to the LR and TVR populations (2-8 km), this
was a surprising difference. Marked differences in everything from body size to
physiology have been documented in rattlesnakes (Beaupre 1995). However, the rock
rattlesnake populations that Beaupre (1995) studied were at significantly different
elevations, which may have accounted for the observed differences. Our study sites are
very similar in elevation, varying by no more than 750 m, with significant overlap in
elevations among sites. We are beginning to investigate other potential differences in
these geographically close populations. For example, preliminary data suggest that tiger
rattlesnakes at the TVR site eat predominantly small mammals, but snakes at the Rocking
K site eat a greater proportion of lizards. We have recently begun microsatellite DNA
analyses to explore these differences in more detail.
Morphology
Raw data for all snakes are shown in Appendix A. We summarized processing data for
all snakes and all sites combined (Table 4), and by gender and age class for each site
(Table 5).
Tiger Rattlesnake Ecology and Management – Goode & Wall 18
Table 4. Morphometric data (mean ± standard error) for all tiger rattlesnakes from all sites
combined from 1997-2001. All lengths and widths are in millimeters (mm).
All Sites Combined
Parameter Females Males
N 52 117
Percent adult 81% 89%
Snout-vent length* 573 ± 10 650 ± 10
Tail length* 40 ± 3 61 ± 3
Mass* 192 ± 9 287 ± 11
Head length 25 ± 2 27 ± 2
Head width 19 ± 1 20 ± 2
Number of segments 7 ± 2 7 ± 1
Rattle length 31 ± 3 35 ± 3
Percent with broken rattle 61% 81%
* = significant at a = 0.05
Snout-vent length varied by sex and by site (Figure 8). Males were longer (F = 16.50, df
= 1, p < 0.0002), heavier (F = 11.69, df = 1, p < 0.0013), and more massive per unit body
length than females. Males had 50% longer tails than females, and the ratio of tail length
to SVL was greater in males (t = 19.71, df = 167, p < 0.0001). Simple regression
revealed that there was no overlap in the range of tail to SVL ratio between males (1.387
+ 0.0925 (SVL) = tail, r2 = 0.74, n = 116, mean = 61.5 mm) and females (3.797 + 0.064
(SVL) = tail, r2 = 0.80, n = 53, mean = 40.7 mm) indicating that this is a reliable
character for sexing tiger rattlesnakes (Figure 9). Males tend to have both longer and
wider heads than females, but not relative to their body size.
Most snake species show marked sexual size dimorphism, with males being the larger of
the sexes (Shine 1978). Tiger rattlesnakes appear to conform to this general pattern.
Various hypotheses have been proposed for why males tend to be larger than females.
Among these hypotheses is the assertion that males are larger so they can be more
effective in male-male agonistic encounters (Beaupre & Duvall 1998). However, this
runs counter to the notion that large female body size should be selected for because
Tiger Rattlesnake Ecology and Management – Goode & Wall 19
larger females can give birth to more offspring, which is the case in many snake taxa
(Shine 1978).
Table 5. Body and head size data (mean ± standard error) for all tiger rattlesnake age
classes at all sites combined from 1997-2001. TVR = Tanque Verde Ridge, RK = Rocking K
Ranch, LR = Loop Road, RMFD = Rural Metro Fire Department, F = female, M = male, SA
= subadult, SVL = snout-vent length, TL = tail length, HL = head length, HW = head width.
TVR RK LR RMFD
Parameter F M SA F M SA F M SA F M
N 14 24 1 13 34 16 10 30 2 5 16
SVL 627
± 6
659 ±
8
511 605 ±
7
667 ±
8
479 ±
10
604 ±
7
687 ±
8
511 ±
7
575 ±
8
678 ±
8
TL 44 ±
2
61 ±
3
38 42 ±
2
64 ±
2
41 ±
3
42 ±
2
66 ±
3
42 ±
3
42 ±
2
63 ±
3
Mass 244
± 7
287 ±
9
113 179 ±
5
295 ±
9
91 ±
7
233 ±
8
341 ±
9
139 ±
7
240 ±
9
327 ±
11
Mass/SV
L
0.38
9
0.436 0.221 0.296 0.442 0.190 0.386 0.496 0.272 0.417 0.482
HL 27 ±
1
27 ±
2
25 26 ±
1
28 ±
1
22 ±
2
26 ±
2
28 ±
1
26 ±
1
24 ±
1
28 ±
1
HW 20 ±
1
21 ±
2
17 19 ±
1
21 ±
1
17 ±
1
20 ±
1
21 ±
1
21 ±
1
19 ±
1
21 ±
1
HL/SVL 0.043 0.041 0.048 0.043 0.042 0.045 0.043 0.040 0.050 0.041 0.041
Tail length is often used to distinguish between sexes in snakes. Presumably, males have
longer tails to accomodate their reproductive organs which are located in the tail.
Another character used to sex snakes is number of subcaudal scales, with females having
fewer subcaudals due to their shorter tail length. However, we observed some overlap in
the number of subcaudals, suggesting that tail length relative to SVL may be a more
reliable way to sex some snake species.
Reproduction
We observed reproductive activity (accompaniment, courtship, and copulation) only
during the summer monsoon season (Table 6). We defined the monsoon season as
beginning when the study area received its first substantial rainfall and ending when it
received its last rainfall. In all years, the onset of the monsoon season was obvious due to
a marked change from extremely dry to extremely humid weather conditions. Not
surprisingly, we also determined that adult males produce semen more during this period
(July-September) than during the spring or fall (Figure 10). Both males and females
Tiger Rattlesnake Ecology and Management – Goode & Wall 20
Adult Size by Site
560
580
600
620
640
660
680
700
0 1 2 3 4 5
Site
SVL (mm)
Male
Female
RK TVR LR RMFD
Figure 8. Adult size by sex at all four sites from 1997-2001. RK = Rocking K Ranch;
TVR = Tanque Verde Ridge; LR = Loop Road; RMFD = Rural Metro Fire Department.
Figure 9. Graph showing the ratio of tail length (TL) to snout-vent length (SVL) in male
tiger rattlesnakes (n = 169). Females (squares) exhibited no overlap with males
(triangles) indicating that TL to SVL ratio is a reliable character for determining sex in
tiger rattlesnakes. See text for equations and t-statistics.
0
10
20
30
40
50
60
70
80
400 450 500 550 600 650 700 750 800
SVL (mm)
TL (mm)
Males
Females
Tiger Rattlesnake Ecology and Management – Goode & Wall 21
Table 6. Date ranges by year of tiger rattlesnake reproductive activity (accompaniment,
courtship, and copulation) compared to annual date ranges for the wet summer season.
Year Reproductive Activity Monsoon Season
1997 08/27 – 09/06 07/17 – 09/11
1998 07/08 – 09/22 07/03 – 09/11
1999 07/26 – 09/05 06/26 – 09/04
2000 -- 06/17 – 09/11
2001 07/30 – 08/17 07/03 – 09/14
Total 07/08 – 09/22 06/17 – 09/14
Semen Present By Season
1 2
51
6 8
18
107
27
0
20
40
60
80
100
120
Mar-April May-June July-Sep Oct-Dec
Season
N
Figure 10. Seasonal incidence of semen expressed from the hemipenal shafts of male tiger
rattlesnakes at all four sites from 1997-2001. White bars = semen present, black bars = all
captures and recaptures combined.
paired with multiple partners (range = 2-5 partners) over the course of a single breeding
season. Reproductive associations of male and female snakes lasted an average of 3.8
days (range = 1-9 days). In some cases, a male snake appeared to follow the same female
over the course of a few to several days. In 1997, we were alerted by a resident living at
the park boundary that a pair of tiger rattlesnakes was mating in his yard. We captured
Tiger Rattlesnake Ecology and Management – Goode & Wall 22
and implanted radiotelemeters into both animals. The male proceeded to follow the
female over the course of several days, and we found him courting her on multiple
occasions. Mating interactions between radiotagged individuals occurred on several
occasions during 1998, a year of high reproductive activity, which coincided with a year
in which we were radiotracking several male and female tiger rattlesnakes.
Overall, we observed tiger rattlesnakes engaged in some manner of reproductive activity
3.6% of the time (range = 0%-7.8%) when located. Far more reproductive activity
occurred in 1998 than in any other year (Figure 11). A greater proportion of females
gave birth in 1999 than in other years as well (Figure 12), providing further evidence that
1998 was an important breeding year (litters are born the year after mating takes place).
Reproductive Activity by Year
1
22
4
0
3
4
18
1
0
1
0
10
1
0 0
0
5
10
15
20
25
1997 1998 1999 2000 2001
Year
N
Accompaniments
Courtships
Copulations
Figure 11. Tiger rattlesnake reproductive activity by year at the Tanque Verde Ridge study
site from 1997-1999 and at the Tanque Verde Ridge and Rocking K study sites combined
from 2000-2001.
Based on palpation of 15 gravid females, we determined average tiger rattlesnake litter
size to be 3.4 ± 1.0 (SD) (range = 2-6). The actual number of young born is probably
lower than our estimates, however, since we mostly performed follicle counts and not all
follicles are ovulated. In any case, the exact number is small compared to litter sizes of
other rattlesnake species found in Arizona (Table 7). Based on five females, which we
captured to assess their reproductive condition, parturition occurred from August 1 to
August 20. We were only able to obtain morphological data on one litter consisting of 5
neonates, which were born to a snake captured by RMFD personnel (Table 8). Neonates
from this litter first shed their skin 8-9 days post-parturition.
Tiger Rattlesnake Ecology and Management – Goode & Wall 23
Proportion Giving Birth
0
5
10
15
20
25
1997 1998 1999 2000 2001 2002
Year
N
Figure 12. Number and proportion of tiger rattlesnakes giving birth by year at the Tanque
Verde Ridge and Rocking K study sites from 1997-2001. White bars = gave birth; black
bars = did not give birth.
Table 7. Average litter size of several rattlesnake species in Arizona (from Lowe et al. 1986).
Species Average Litter Size
Crotalus. atrox 9
C. viridis 9
Sistrurus catenatus 9
C. scutulatus 8
C. cerastes 7
C. molossus 7
C. mitchellii 5
C. willardi 5
C. pricei 5
C. lepidus 4
C. tigris 3.4 ± 1.0 (range 2-6)
Tiger Rattlesnake Ecology and Management – Goode & Wall 24
Table 8. Morphological data (mean ± standard error) for the litter born to CRTI #55, a
female collected by the Tucson Rural-Metro Fire Department in 1999.
Littermate Born First
Shed
Sex SVL TL Mass HL HW
1 8/1/99 8/10/99 M 259 25.0 19.5 17.5 13.5
2 8/1/99 8/9/99 M 262 26.0 21.2 19.0 13.5
3 8/1/99 8/9/99 M 265 24.1 21.0 19.0 13.0
4 8/1/99 8/9/99 M 263 24.0 21.5 18.0 13.0
5 8/1/99 8/9/99 F 261 20.8 22.0 20.0 13.0
Mean 4M:1F 262
±
1.5
24.0
±
1.4
21.0
±
0.97
18.7
±
0.99
13.2
±
0.52
On average, adult females give birth once every three years as indicated by the fact that
only 33% of females captured during the course of this study were gravid. However,
there was significant individual and annual variation. For example, more than half of the
adult females we processed in 1999 produced a litter in that year, and two snakes gave
birth in both 1998 and 1999. Gravid snakes are not significantly longer than non-gravid
adult females (t = 0.96, df = 42, p < 0.34), but as expected, they are significantly heavier
(t = 2.30, df = 38, p < 0.03) (Table 9). One gravid female we found measured 521 mm
SVL, the smallest reproductively mature tiger rattlesnake yet recorded (cf. Goldberg
1999).
Table 9. Size (mean SVL ± standard error) of adult female tiger rattlesnakes that became
gravid at any time during the study compared to size of females who were never found to be
gravid, and to all adult females. Data are from all sites combined from 1997-2001
Category SVL Mass N
Gravid Females 602 ± 7 245 ± 8 16
Non-Gravid Females 612 ± 7 211 ± 7 26
All Adult Females 608 ± 7 221 ± 8 42
Tiger rattlesnakes mate during the monsoon season. Females store sperm over the
winter, ovulate upon emergence from their dens in the spring, and gestate until late July
or early August, when they give birth. Spermatogenesis commences in late spring or
early summer, and females initiate vitellogenesis during the summer monsoon of a
reproductive year.
The type of mating system in effect is difficult to determine because of the variation in
both male and female reproductive behavior. Tiger rattlesnakes may exhibit prolonged
Tiger Rattlesnake Ecology and Management – Goode & Wall 25
mate-searching polygyny (PMSP), characterized by females that are irregularly spaced,
difficult to locate, and/or infrequently receptive (Duvall et al. 1992). Under this system,
males find few if any females during the mating season and rarely encounter other males,
resulting in very little male-male agonistic behavior (i.e., combat). We did not observe
combat during the five-year study, and males in most years found only a single female, or
no females at all.
In contrast, female defense polygyny (FDP), in which females are easier to locate, more
abundant, and/or sexually receptive for longer periods of time (Duvall et al. 1992), may
best describe the mating system in tiger rattlesnakes. Under FDP, males are expected to
engage in serial mate guarding, attempting to monopolize the reproduction of multiple
females in succession (Duvall et al. 1992). Males are also more likely to come into
contact with other males, with combat a likely result. Indeed, we observed what
appeared to be mate guarding on multiple occasions, and male-male combat in tiger
rattlesnakes has been observed (P. Holm, pers. comm.). Further, while we witnessed no
combat at our study sites, we did observe a male snake initiate combat behavior as we
attempted to photograph him while copulating with a radiotagged female. The male rose
up to combat our snake tongs while we used them to brush aside vegetation, which was
obscuring our view of the copulating pair.
None of this information is convincing evidence of FDP, however, because long-term
accompaniment does not necessarily represent mate guarding. Courtship and copulation
behavior in male rattlesnakes is cued largely by pheromones that females produce upon
shedding (Schuett 1992). Therefore, it is possible that males that remain with females for
extended periods of time are simply waiting for them to shed. We observed a male
vigorously courting a road-killed female, indicating the importance of chemosensory
information in reproduction. In short, we need more data to determine the precise nature
of the mating system of tiger rattlesnakes.
Tiger rattlesnake reproduction is extremely variable from year to year and appears to be
significantly correlated with rainfall. In 1998, when we observed a dramatic increase in
mating activity, we also received record amounts of rainfall due to a pronounced El Niño
event (Figure 13). Rodents in the desert Southwest are known to breed prolifically
following intense rainy seasons, in particular after abnormally wet winters (Y. Petryszyn,
pers. comm.).
It is possible that female tiger rattlesnakes benefited from an elevated prey base in the
spring and summer of 1998, accumulating sufficient fat reserves to initiate the
energetically costly process of vitellogenesis. Snakes at our study sites averaged one
litter every three years, but reproduction varied greatly from individual to individual.
Two females gave birth in successive years (1998 and 1999), indicating that tiger
rattlesnakes can reproduce annually if females have sufficient energy reserves.
Tiger Rattlesnake Ecology and Management – Goode & Wall 26
Rainfall by Season and Year
0
100
200
300
400
500
600
1997 1998 1999 2000 2001
Year
mm
Wet Summer
Winter
Figure 13. Seasonal rainfall by year at Saguaro National Park. Data are presented in
“water years” meaning that the year begins at the onset of winter rains and ends when the
summer rains end.
Growth
Females and males did not differ in annual growth rate (t = 0.58, df = 38, p = 0.57). Both
sexes averaged a yearly SVL increase of 2.5%. Not surpisingly, virtually all growth
occurred during the snakes’ active season (April-early November) rather than over the
winter, when no feeding took place (Figure 14).
We observed growth-rate differences between sites. Snakes at TVR grew more than
twice as fast as snakes at the RK (Figure 15); however, these differences were not
statistically significant (F = 2.57, df = 33, p = 0.14). Site differences in growth rates may
be a consequence of divergent diets at the two sites. Snakes at TVR consumed primarily
small mammals, relatively large prey with a high energy yield, while tigers at RK ate
mostly lizards (see below). Thus, snakes at TVR may be accruing more energy, and as a
result may be able to devote more resources to growth.
Tiger Rattlesnake Ecology and Management – Goode & Wall 27
SVL Growth by Season
2.21
0.30
0
1
2
3
Winter Active Season
%
Figure 14. Mean annual growth in SVL for all tiger rattlesnakes combined, 1997-2001.
Average SVL Growth/Year
2.8
1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
TVR RK
Site
%
Figure 15. Average growth rate per year of all tiger rattlesnakes combined by site.
Tiger Rattlesnake Ecology and Management – Goode & Wall 28
Our data suggest that implantation of radiotelemeters may retard growth in tiger
rattlesnakes. Snakes without radios grew more than twice as rapidly as snakes with
radios (F = 8.96, df = 37, p = 0.01; Figure 16). Perhaps implanted snakes spend more
time basking to recover from surgery, compromising other activities such as foraging. It
seems reasonable to assume that some energy must be allocated to healing at the expense
of growth. Indeed, snakes with radios shed more often than those without (1.3 sheds/year
and 1.1 sheds/year respectively), although this difference was not statistically significant
(t = 1.39, df = 24, p = 0.18). Shedding in response to injury is a known response in
snakes (Rubio, 1998).
However, short-term effects of surgery are not likely to be a major factor in growth-rate
disparity, because snakes that had been implanted for two years still exhibited diminished
growth. Perhaps the radiotag implant is constantly being “fought off” by the snakes
immune system. Such a prolonged heightened immune response would of course require
energy. It is also possible that the bulk of the transmitter may render the snake less
mobile and as a result, less able to obtain prey. At this point, we cannot definitively say
Average SVL Growth/Year
1.5
3.9
0
1
2
3
4
5
Radio Snakes NR Snakes
%
Figure 16. Average growth rate of tiger rattlesnakes implanted with a radiotag (Radio
Snakes) and snakes without a radiotag implant (NR Snakes). Although snakes without
implants grew more than twice as much as snakes with implants, the results were not
statistically significant (t = 0.61, df = 51, p < 0.512) due to high individual variation in
growth rates.
Tiger Rattlesnake Ecology and Management – Goode & Wall 29
how transmitter implantation impacts tiger rattlesnake growth (or any other aspect of
their biology). More research is needed to determine how the powerful and increasingly
pervasive technique of radiotelemetry is affecting the biology and behavior of study
organisms. Recognizing that effects of radiotelemetry implants may be negative is
important, because it enables us to better determine potential sources of error in our data.
Spatial Ecology
We implanted radiotelemeters into 35 tiger rattlesnakes, which we located 2627 times
(Figure 17). We utilized several movement and space-use parameters to compare the
spatial ecology of males and females (Table 10). Females had smaller home ranges than
males (Table 10; Figure 18), which is not surprising given that in most rattlesnake species
males actively search for relatively sedentary female mates (Duvall et al. 1992). Both
sexes exhibited seasonal differences in home range size and movement patterns, with
conspicuous spikes occurring in wet summer, when most feeding and all mating takes
place (Table 10; e.g., Figure 19). However, some seasonal activity differences between
Figure 17. Digitized aerial photograph showing 2627 locations of 35 tiger rattlesnakes at
the Tanque Verde Ridge study area (left) and the Rocking K Ranch study area from 1997-
1998 and 2000-2001. Data for 1999 are not included because of technical difficulties with
GPS post-processing. 1997 = purple, 1998 = orange, 2000 = blue, and 2001 = yellow.
Boundary
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 30
0 2 km
Figure 18. Minimum convex polygon home ranges for selected females (top) and males
(bottom) at the Tanque Verde Ridge and Rocking K study areas. There is substantial
overlap in male home ranges, therefore only the home range outline is displayed.
N
0 1 km
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 31
the sexes were apparent. Females moved more during the spring than males did (Table
10), which may be explained by the fact that females emerged from hibernation an
average of 18 days (April 5 for females as opposed to April 23 for males) sooner than
males did. By May and June (dry summer), males were more active and mobile than
females and remained so until entering their winter dens in late October or November.
Males, but not females, exhibited annual differences in home range size and movement
patterns in 1998 compared to 1997 (Figure 20). As noted above, 1998 was a very wet
year during which a tremendous amount of tiger rattlesnake reproductive activity
occurred. Thus increased male movement in 1998 probably reflected greater mate-searching
activity stimulated by abnormally high rainfall. As female movement patterns
remained relatively constant, differences in foraging behavior from year to year were not
implicated.
We have not yet intensively investigated space use by site, but some differences do seem
to exist. For instance, tiger rattlesnake movements at the RK were of a much more linear
(north-south) nature than at TVR (Figure 17). We believe this is due to topographical
differences between sites. At RK, one major north-south wash drains most of the study
area, while TVR is characterized by a network of arroyos. As tiger rattlesnakes tend to
use washes during the active season (see below), wash orientation probably has an effect
on snake movement patterns.
Feeding and Diet
Prior to this study, the feeding habits of tiger rattlesnakes were not well known. The
species’ small head size has led to the suggestion that it consumes primarily lizards
(Lowe et al. 1986, Ernst 1992). However, data from fecal samples revealed that tiger
rattlesnakes take a variety of prey types and that they appear to feed predominantly on
small mammals (Figure 21).
Both male and female tiger rattlesnakes foraged most actively and most successfully
during the summer monsoon season (Figure 22). However, some gender differences in
diet did exist, although these differences were not statistically different (C2 = 0.89, df = 1,
87, p = 0.35). Males consumed an approximately equal proportion of lizards and rodents,
while females ate more small mammals (Figure 23). This difference is probably not a
consequence of divergence in head or body size, because males are larger than females.
Rather, the difference may result from greater energy requirements of adult females.
Vitellogenesis and embryo development are extremely costly activities; perhaps females
need larger, higher-energy prey than males do. Another possibility is that diet differences
are a residue of activity and movement differences between the sexes. Males move more
frequently and travel greater distances than females, especially during the wet-summer
active season. Therefore, males are likely to encounter more lizards (either active or
resting; see below) than females. Females may be more restricted to rodents by their
more sedentary habits.
Tiger Rattlesnake Ecology and Management – Goode & Wall 32
Table 10. Summary of movement and home range data (mean ± standard error) for tiger
rattlesnakes at Tanque Verde Ridge and Rocking K from 1997-2001 (N = 2627). Data from
individual snakes were not used in the analyses unless the number of radiotelemeter fixed
was at least n = 30.
*Significant at a = 0.05
Season Parameter Males Females
Total Total Distance Moved* 4009 ± 326.4 1578 ± 176.5
Distance/Movement* 92.7 ± 7.3 42.4 ± 6.4
Distance/Day* 22.4 ± 2.4 9.8 ± 1.2
MCP* 15.0 ± 4.2 3.3 ± 0.5
95% Active Kernel* 19.1 ± 4.8 4.6 ± 0.8
50% Core Area* 3.4 ± 0.8 0.9 ± 0.2
Spring Total Distance Moved 130 ± 53.2 219 ± 67.5
Distance/Movement 24.0 ± 8.3 34.8 ± 13.1
Distance/Day 3.7 ± 1.5 6.3 ± 2.0
MCP 0.2 ± 0.2 0.3 ± 0.2
95% Active Kernel 2.6 ± 1.5 3.1 ± 2.6
50% Core Area 0.6 ± 0.4 0.5 ± 0.4
Dry Summer Total Distance Moved* 481 ± 206.2 103 ± 45.2
Distance/Movement 61.9 ± 24.9 11.9 ± 4.2
Distance/Day* 14.6 ± 7.4 2.2 ± 1.0
MCP* 1.5 ± 1.1 0.05 ± 0.02
95% Active Kernel* 2.9 ± 1.0 0.3 ± 0.1
50% Core Area* 0.6 ± 0.2 0.05 ± 0.02
Wet Summer Total Distance Moved* 2142 ±281.4 707 ± 106.9
Distance/Movement* 91.0 ± 11.2 32.6 ± 4.2
Distance/Day* 34.9 ± 4.4 11.4 ± 1.6
MCP* 10.1 ± 1.8 1.7 ± 0.6
95% Active Kernel* 16.9 3.8 3.8 ± 1.3
50% Core Area* 3.0 ± 0.9 0.8 ± 0.2
Fall Total Distance Moved* 1002 ± 263.9 438 ± 61.5
Distance/Movement* 65.3 ± 13.9 30.9 ± 5.1
Distance/Day* 28.4 ± 7.3 11.7 ± 2.0
MCP* 5.0 ± 1.8 0.7 ± 0.1
95% Active Kernel* 15.2 ± 5.9 2.7 ± 0.6
50% Core Area* 3.1 ± 1.1 0.6 ± 0.2
Tiger Rattlesnake Ecology and Management – Goode & Wall 33
Figure 19. Minimum convex polygon home ranges for wet summer compared to the rest of
the year for a male tiger rattlesnake at Tanque Verde Ridge in 1998. This pattern of
seasonal home range use was typical for all tiger rattlesnakes, although more so for males
than for females.
We also observed feeding differences between sites (C2 = 4.73, df = 1, 74, p = 0.03).
Tiger rattlesnakes took more lizards than rodents at RK, but nearly three times more
rodents than lizards at TVR (Figure 24). We did not observe snakes to employ divergent
foraging strategies from site to site. Rather, our data reveal that lizards are simply more
abundant at RK (Table 11).
Of 29 identified lizard remains in tiger rattlesnake feces, 27 were whiptails
(Cnemidophorus species). Whiptails are active, fast-moving diurnal lizards that are
extremely common at RK and less so at TVR (Table 11). The few feeding episodes we
observed, suggest that tiger rattlesnakes ambush whiptails that wander into striking range
(as they do with rodents); however, active searching for sleeping or resting lizards may
also be important. We witnessed what appeared to be active foraging on multiple
occasions, as snakes were observed to move throughout woodrat middens and other
rodent burrow systems, exhibiting increased tongue-flicking.
Wet Summer
Rest of the Year
Tiger Rattlesnake Ecology and Management – Goode & Wall 34
Figure 20. Minimum convex polygon home ranges for selected males (top) and females
(bottom) at the Tanque Verde Ridge study area in 1997-1998. Male home range size varied
in size from year to year, but female home range size did not.
1997
1998
1998
1997
N
0 1 km
1997
1997
1998
1998
N
0 1 km
Tiger Rattlesnake Ecology and Management – Goode & Wall 35
Figure 21. Percent of prey types in tiger rattlesnake diet for 105 tiger rattlesnakes from all
sites combined from 1997-1999.
Percent Bolus by Season
0%
5%
10%
15%
20%
25%
March-April May-June July-September October-November
Season
Figure 22. Percentage of tiger rattlesnakes (all sites and all years combined) found to
contain a food bolus in their gastrointestinal tract at different times of the year. Food boli
were detected via external palpation.
Tiger Rattlesnake Diet
0
10
20
30
40
50
60
Mammal Reptile Avian No prey
Prey Type
%
Tiger Rattlesnake Ecology and Management – Goode & Wall 36
Diet By Sex
0
10
20
30
40
50
60
70
Females (N=33) Males (N=52)
Relative Proportion (%)
Rodents
Lizards
Figure 23. Proportion of male and females tiger rattlesnakes eating rodent and lizard prey
at all site and in all years combined.
Table 11. Relative abundance, by site, of lizard species (all except Heloderma suspectum)
considered potential prey of tiger rattlesnakes.
Lizard Category TVR RK Total
Prey lizards 364 527 891
Cnemidophorus individuals 149 227 376
Prey lizards/hour search effort 0.48 1.56 0.81
Cnemidophorus individuals/hour search effort 0.19 0.68 0.34
Tiger Rattlesnake Ecology and Management – Goode & Wall 37
Diet By Site
37
14
16
21
0
5
10
15
20
25
30
35
40
45
TVR RK
N
Rodents
Lizards
Figure 24. Number of tiger rattlesnake fecal samples containing rodent and lizard remains
by site.
Habitat
Logistic regression analysis performed on microhabitat data from 1997 revealed
differences in habitat use between sexes that varied by habitat type (uplands [= slope and
ridge] versus lowlands [= wash and bajada]) (Table 12). The differences were based on
comparison with random locations within tiger rattlesnake home ranges. In lowlands,
female tiger rattlesnakes were associated with significantly greater shrub, tree and canopy
cover than males. Males were found more often in prickly pear cactus than females and
males were also found closer to woodrat middens. In uplands, females were associated
with greater grass and tree cover than males.
These results seem to reflect the tendancy for females to remain in cover more often than
males, which is likely a byproduct of males’ tendancy to move more often than females.
Increased movement on the part of males is in turn related to the fact they must actively
search for more sedentary females in order to obtain mating opportunities. Likewise, the
tendancy for males to be found in association with woodrat middens reflects their
predilection to actively forage, whereas females ambush more often (see Diet and
Feeding).
Tiger Rattlesnake Ecology and Management – Goode & Wall 38
Table 12. Logistic regression analysis of microhabitat data for locations (N = 203) of 10
tiger rattlesnakes, Tanque Verde Ridge site, 1997. Lowlands = wash and bajada, uplands =
slope and ridge. P>F = ANOVA, P>C2 =Kruskal-Wallis ANOVA on ranks, which was used
to determine final probabilities because the variables were not normally distributed.
*P < 0.10
**P < 0.05
Tiger rattlesnakes exhibited pronounced seasonal differences in habitat use (Figure 25).
The typical pattern consisted of very low activity in spring and dry summer as snakes
remained mostly on rocky slopes with some individuals moving into washes. We
observed a dramatic increase in movment during wet summer as snakes primarily used
wash and bajada areas to forage and mate. In fall, tigers continued to move, although less
so than in wet summer, as snakes made their way back to their winter dens located on
rocky slopes above washes and bajada areas.
Lowlands
Category Male Female P>F P>C2 Sex
Midden Distance 3.68 6.13 0.057 0.058* F
% Exposed 31.18 30.78 0.964 0.962
% Litter 18.82 5.81 0.039 0.754
% Grass 14.41 18.75 0.581 0.501
% Forb 1.47 4.09 0.514 0.416
% Shrub 3.23 24.77 0.021 0.063* F
% Tree 0.59 7.73 0.040 0.009** F
% Cactus 30.29 12.16 0.009 0.004** M
% Canopy 10.00 23.00 0.081 0.086* F
Uplands
Midden Distance 6.26 5.33 0.589 0.693
% Exposed 62.12 52.14 0.229 0.294
% Litter 4.24 9.05 0.377 0.360
% Grass 0.76 7.38 0.051 0.088* F
% Forb 6.36 2.62 0.292 0.189
% Shrub 10.30 12.86 0.682 0.984
% Tree 0.76 4.52 0.024 0.051* F
% Cactus 15.45 11.43 0.497 0.231
% Canopy 10.15 9.76 0.954 0.800
Tiger Rattlesnake Ecology and Management – Goode & Wall 39
Figure 25. Tiger rattlesnakes exhibit pronounced seasonal variation in movement patterns
and habitat selection. The habitat map (top) shows a subset of tiger rattlesnake locations
from 1997-1998. The histogram (bottom) shows the proportion of tiger rattlesnake
locations relative to availability of each habitat type.
0
10
20
30
40
50
60
70
Wash Bajada Slope Ridge
%
Available
Spring
Dry Summer
Wet Summer
Fall
Bajada
Plateau
Slope
Ridge
Wash
N
0 250 m
Tiger Rattlesnake Ecology and Management – Goode & Wall 40
Small-Mammal Trapping
Small mammal diversity varied by habitat type at our study sites (Table 13). Although
relative abundance of small mammals varied by habitat type, we were unable to precisely
quantify the differences using mark-recapture data because sample sizes were low. We
had hoped to draw conclusions regarding potential interactions of tiger rattlesnakes and
their small-mammal prey, but dismal trapping success made it difficult. However, we did
document distinct changes in species composition among habitat types. For example,
Chaetodipus intermedius is only found on rocky slopes and ridges, while C. penicilatus is
only found in wash and bajada areas.
These habitat differences may play a role in tiger rattlesnake foraging ecology. We may
be able to address this more thoroughly as we progress with our fecal analyses.
Presumably, we will be able to pinpoint more accurately the rodent species consumed by
tiger rattlesnakes. This will allow us to say more about the effect of habiat type on tiger
rattlesnake diet, which we can then couple with information on season, sex, reproductive
status and body size.
Table 13. Small mammals trapped at the Tanque Verde Ridge site from 1998-1999. CHBA
= Chaetodipus baileyi, CHPE = Chaetodipus peniculatus, CHIN = Chaetodipus intermedius,
PEAM = Perognathus amplus, PEER = Peromyscus eremicus, NEAL = Neotoma albigula.
Habitat
Type Species
Number
Caught
Number
Recaptured
Population
Estimate 95% CI
Wash
Slope
Ridge
Bajada
CHBA
CHPE
CHIN
PEAM
PEER
CHBA
CHPE
CHIN
NEAL
PEER
CHBA
CHIN
PEER
NEAL
CHBA
CHPE
NEAL
50
22
1
7
2
5
3
9
12
6
2
18
4
2
7
17
3
11
15
0
4
0
19
1
1
1
2
2
5
4
1
2
13
0
15
7
23
31
21
14-25
7-17
10-105
23-55
19-33
Tiger Rattlesnake Ecology and Management – Goode & Wall 41
Lizard Abundance Index
We incidentally encountered a total of 46 reptile and amphibian species at TVR and RK
(Table 14), 16 of which were lizards. Lizard species composition differed little between
Table 14. Numbers of individuals and hours required to encounter an individual of all
reptile and amphibian species encountered incidentally at both the TVR and RK sites from
1997-2001.
Species Number of Individuals Hours/Individual
Arizona elegans 1 2550
Bufo alvarius 17 150
Bufo cogntus 2 1275
Bufo punctatus 13 196
Callisaurus draconoides 59 43
Chilomeniscus cinctus 1 2550
Cnemidophorus burti 1 2550
Cnemidophorus flagellicaudus 5 510
Cnemidophorus spp. 279 9
Cnemidophorus tigris 90 28
Cophosaurus texanus 80 32
Coleonyx variegatus 6 425
Crotalus atrox 62 41
Crotalus molossus 5 510
Crotalus scutulatus 1 2550
Crotaphytus collaris 9 283
Eumeces fasciatus 1 2550
Gopherus agassizi 60 43
Heloderma suspectum 37 69
Hyla arenicolor 1 2550
Hypsiglena torquata 3 850
Kinosternon sonoriense 1 2550
Lampropeltis getula 6 425
Leptotyphlops humilis 1 2550
Masticophis bilineatus 13 196
Masticophis flagellum 9 283
Micruroides euryxanthus 3 850
Phrynosoma solare 14 182
Pituophis catenifer 2 364
Rana catesbeiana 1 2550
Rana yavapaiensis 1 2550
Rhinocheilus lecontei 17 150
Salvadora hexalepis 8 319
Sceloporus clarki 80 32
Tiger Rattlesnake Ecology and Management – Goode & Wall 42
Table 14 (con’t.)
Species Number of Individuals Hours/Individual
Scaphiopus couchi 9 283
Sceloporus magister 20 128
Sceloporus spp. 4 638
Thamnophis cyrtopsis 11 232
Urosaurus ornatus 167 15
Uta stansburiana 81 31
sites; we found 15 species at TVR and 13 at RK, and only three (Cnemidophorus burti,
Crotaphytyus collaris, and Eumeces obsoletus) were observed at one site but not the
other. However, obvious differences in lizard relative abundance between sites were
apparent. Lizards were much more common at RK than at TVR. Furthermore, known or
potential prey species (which we defined as all species except Heloderma suspectum
based on body size) were more abundant at RK (Table 11). This pattern held for
whiptails (Table 11), an important prey item of tiger rattlesnakes (see above).
Like tiger rattlesnakes, lizards (including whiptails), were most active and most
commonly observed during the monsoon season (Table 15). Although potentially biased,
because we
Table 15. Relative abundance and encounter rate of tiger rattlesnake prey lizards by season
(season determined by month) at the TVR and RK sites. DS = dry summer; WS = wet
summer.
Season TVR RK Total
Radiotracking
Hours
Prey Lizards/
Tracking Hour
Spring (Mar-Apr) 40 0 40 83 0.48
DS (May-June) 63 89 152 189 0.80
WS (July-Sept) 254 390 644 562 1.15
Fall (Oct-Nov) 3 44 47 206 0.23
Winter (Dec-Feb) 4 5 9 59 0.15
often used washes to travel from site to site, lizards also seemed to favor washes (Table
16), a preference shared by tiger rattlesnakes during their active season. Tiger rattlesnake
activity periods and habitat preferences may therefore have evolved at least in part to take
advantage of lizard prey.
Tiger Rattlesnake Ecology and Management – Goode & Wall 43
Table 16. Relative abundance of tiger rattlesnake prey lizards by habitat type at the TVR
and RK sites from 1997-2001.
Habitat Type TVR RK Total
Bajada 18 52 70
Ridge 11 42 53
Slope 21 113 134
Wash 116 174 290
MANAGEMENT IMPLICATIONS
In addition to studying tiger rattlesnake natural history and ecology, our objective was to
use this knowledge to develop more effective management strategies for rattlesnakes in
general. The results of this research have implications for rattlesnakes that live along the
boundaries of parks and preserves and that move into adjacent urbanized areas. In
addition, our results lead to possible management strategies for how to mitigate the
effects of translocating rattlesnakes away from urbanized areas. And finally, our findings
enable us to predict how the impending Rocking K development may affect rattlesnakes
living in the area.
The TV site is situated along the boundary of SNP adjacent to a low-density residential
housing area. Several radiotelemetered tiger rattlesnakes moved in and out of the park
during the course of the study, and several more non-radiotelemetered snakes were either
captured on private land or found by residents on their property (Figure 26). The
community living along the park boundary at this site has been there for decades, and the
residents living there are very enlightened when it comes to living with wildlife. Several
residents expressed a keen interest in our research and even professed to be rattlesnake
enthusiasts. However, some residents still insisted on killing rattlesnakes found in their
yard. In general, however, the combination of environmentally sensitive landowners and
a low density of residents may bode well for rattlesnakes. Our radiotagged snakes were
found repeatedly in and around peoples’ yards without incident. Most houses in the area
are on lots of 5-40 acres, which seems to give the rattlesnakes plenty of space to move in
without contacting people on a frequent basis. Furthermore, there is only one main road
that provides access to the housing area and it is neither paved, nor does it pass through
tiger rattlesnake habitat. The lack of roads in the area further allows for peaceful
coexistence of rattlesnakes and humans.
When low-density housing areas abut large natural areas, it would appear that
rattlesnakes have a reasonable chance of persisting indefinitely. Of course, this is not
always the situation. In many areas surrounding Tucson and Phoenix, much higher
density urban areas abut parks, preserves, and national forest lands. Many of the
Tiger Rattlesnake Ecology and Management – Goode & Wall 44
residents living in these areas are new to the desert and are unfamiliar with rattlesnakes
and other wildlife. This can lead to a situation in which rattlesnakes may be killed or
humans may be bitten.
Figure 26. Digitized aerial photograph showing the movements of 6 radiotelemetered tiger
rattlesnakes that moved beyond the boundaries of Saguaro National Park during the course
of the study. A total of 12 tiger rattlesnakes were found outside the park boundary,
including 4 snakes that were found by residents living along the edge of the park.
In the near future, SNP will experience unprecedented development along its southern
boundary due to the Rocking K development (Rocking K Specific Plan 1991, 1996). It
seems reasonable to apply what we have learned during the course of this study to predict
the effects of the development on rattlesnakes living in the area. Our pre-development
data seem to point to some obvious predictions. For example, the extensive bajada area
at the north end of the main xeroriparian wash at the RK site will eventually be home to a
large, high-end resort. This area is relatively flat and less rocky, making it much easier
and less costly to develop. Mass grading to make room for a huge building will certainly
leave this area uninhabitable by snakes. Based on movement and home range data, this
bajada area has been used intensively by tiger rattlesnakes. Snakes use this area as they
move from winter den sites on south-facing slopes within the park to the xeroriparian
wash south of the park boundary (Figure 27). The wash is an important area where
snakes congregate in the summer to forage and mate. The resort will effectively cut off
this corridor between the snakes’ winter and summer habitats. We expect the incidence
Boundary
N
0 250 m
Houses
Tiger Rattlesnake Ecology and Management – Goode & Wall 45
of tiger rattlesnake observations in and around the resort to be very high because of its
location between these two critical habitat areas.
Figure 27. Digitized aerial photograph showing movements
of 16 tiger rattlesnakes in relation to the park boundary and
the future site of the Rocking K development resort. Snakes
overwinter on steep slopes and travel through the future
resort site on their way to and from wash and bajada areas.
The movement of rattlesnakes into the developed area sets the stage for what we expect
to be a critical management concern in the future. The primary issue is what to do when
people living, working, and recreating in the area encounter rattlesnakes. One approach
Future
Resort
Site Wash
Slope
Bajada
Tiger Rattlesnake Ecology and Management – Goode & Wall 46
has been to destroy so-called “nuisance” rattlesnakes that come in contact with people.
Killing rattlesnakes is undoubtedly not good for the snakes themselves, and may pose a
threat to the person attempting to kill the snake. Many rattlesnakes, which were
presumed dead, have managed to bite their assailant. Therefore, killing rattlesnakes is
not likely to be an effective option.
Another tactic for dealing with nuisance rattlesnakes, which is the current preferred
method, is to translocate the snakes away from populated areas (Nowak and van Riper
1999). The Rural Metro Fire Department (RMFD) removes an estimated 3,000-5,000
rattlesnakes from the yards of residents living in and around Tucson every year (G. Good,
RMFD, personal communication). The translocation of rattlesnakes has become an
important management concern for a variety of reasons. Rattlesnakes are venomous and
they may pose a serious threat to people living in areas where rattlesnakes are abundant
(although the threat of snakebite is almost always exaggerated). The real victims of
translocation are the snakes themselves. Translocated rattlesnakes show aberrant
movement patterns, and some individuals may even succumb to being translocated
(Reinert and Rupert 1999). Our data indicate that tiger rattlesnakes show remarkable
fidelity to their home ranges, using the exact same rock outcrops, wood rat middens and
even individual shrubs throughout the course of the year and in successive years.
Aberrant movement patterns may be the result of translocating a snake out of its home
range, causing the snake to become disoriented. This can result in even greater
movement by snakes, thereby increasing the chance that they will find their way into
someone’s backyard. Potential effects on snakes residing in areas where translocated
snakes are released are unknown. However, it seems likely that the addition of new
individuals into the area will be detrimental if resources cannot support an increase in the
number of snakes present.
Many tiger rattlesnakes spent the winter on lower elevation slopes and rock outcrops
situated in and around the area slated for development. If these rocky habitats are
removed to make way for the resort and houses, then this is expected to have a negative
impact on any snakes that currently use these areas as winter refugia. Because these
rocky areas are so critical to the life history of tiger rattlesnakes, damage to these areas
should be of heightened concern to wildlife managers and land planners.
Another specific example of how the development may be expected to impact tiger
rattlesnakes is based on the location of the golf course, with fairways placed along the
wash corridor. Tiger rattlesnakes use the wash corridor for foraging and breeding
purposes during the summer active season. This habitat will be virtually eliminated when
replaced by wide-open fairways that provide little or no cover for snakes (or wildlife in
general). This ties into yet another management concern related to the potential effects of
the development on tiger rattlesnake prey. If the diversity, abundance and distribution of
lizards and rodents are altered by the development, then tiger rattlesnake movements and
habitat use can also be expected to change. For example, the primary prey source of tiger
rattlesnakes at RK is whiptail lizards (M.J. Goode, unpublished data), which prefer open
Tiger Rattlesnake Ecology and Management – Goode & Wall 47
desert areas with intermittent shrub cover. Fairways and parking lots are not expected to
support large populations of whiptail lizards, which may result in a reduction of tiger
rattlesnake prey availability. On the other hand, increased water and vegetation
associated with the development may attract rodents, which may in turn attract
rattlesnakes, thereby exacerbating the nuisance rattlesnake problem. In either case, the
effects of the development on rattlesnake prey resources will likely be long term and
subtle, making the effects more difficult to detect.
Predicting the effects of the development on tiger rattlesnakes is speculative, but may
provide an important guide when developing areas in which they live. As for
determining the actual effects of the development on rattlesnakes, we now have critical
baseline data at RK and at the TVR control site within SNP. This will enable us to more
precisely quantify the effects when the development occurs. Only through this rigorous
scientific approach will we be able to make an unbiased assessment of the effects of
urban development on tiger rattlesnakes. These findings can then be applied to other
areas planned for development that abut natural areas such as SNP.
A MANAGEMENT PLAN FOR URBAN RATTLESNAKES
We have identified several threats facing rattlesnakes living in urban and urbanizing
areas. In this section, we list these threats, followed by specific goals and strategies for
removing or mitigating the threats. We also provide information on actions that have
been taken to achieve these goals.
THREAT DIRECT KILLING OF “NUISANCE” RATTLESNAKES
GOAL Educate public about differences between real and perceived threats of
living in proximity to rattlesnakes.
Encourage fire department personnel to inform the public about the risks
(e.g., being bitten) involved in attempting to kill rattlesnakes.
Work with Arizona Poison Control Center at the University of Arizona to
educate the public about the risks of living in proximity to rattlesnakes and
about the proper procedures for how to deal with snakebite.
Inform public of Arizona Game and Fish regulations requiring a hunting
license to kill rattlesnakes.
STRATEGY Develop an educational brochure to distribute to residents living in areas
where rattlesnakes are common.
Tiger Rattlesnake Ecology and Management – Goode & Wall 48
Develop an educational video depicting rattlesnake defensive behaviors
and how they vary by species and ecological context (e.g., distance to
cover, temperature).
Develop interpretive signage at golf courses that include information
about the natural history and ecology of rattlesnakes.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property.
We are currently developing a video depicting typical defensive behavior
of three rattlesnake species that can be used to educate people about what
to expect when they encounter a rattlesnake. It is our belief that wanton
killing of rattlesnakes is mostly due to ignorance perpetuated by myths
and misunderstandings associated with the true nature of rattlesnake
behavior.
Our association with Jude McNally of the Arizona Poison Control Center
goes back nearly 10 years. We have been featured together on several
media events and have worked together to inform the public about
rattlesnakes and the issue of snakebite in general.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Dennis Caldwell, a graphic designed specializing in
herpetofauna, has created and presented examples of signs to the
development supervisor who is in the process of deciding to proceed with
the project.
THREAT TRANSLOCATION OF “NUISANCE” RATTLESNAKES
GOAL Translocate rattlesnakes within their home ranges whenever possible.
Inform and educate public about the spatial ecology of rattlesnakes,
including characteristics of home ranges, typical movement and activity
patterns, and especially, the extreme fidelity that rattlesnakes show to their
home ranges.
Encourage fire department personnel to inform the public about
rattlesnake home range fidelity and to adopt a policy of translocation
within home ranges whenever possible.
Tiger Rattlesnake Ecology and Management – Goode & Wall 49
Work with Arizona Poison Control Center at the University of Arizona to
educate the public about rattlesnake spatial ecology, and to advocate
translocation within home ranges.
STRATEGY Develop an educational brochure that provides information on rattlesnake
spatial ecology to distribute to residents living in areas where rattlesnakes
are common.
Work with fire departments besides RMFD to educate them about
rattlesnake spatial ecology and behavior, and conduct trainings for firemen
to properly translocate rattlesnakes.
Develop an educational program in conjunction with the Arizona Poison
Control Center that focuses on rattlesnake translocation procedures.
Data gathered during the course of this study indicate that tiger
rattlesnakes show very little annual difference in home range location and
use. These data can be used to bolster recommendations to translocate
snakes within their home ranges.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property. This
brochure also contains information about translocation of rattlesnakes.
We are currently developing a video depicting typical defensive behavior
of three rattlesnake species that can be used to educate people about what
to expect when they encounter a rattlesnake. We could easily include
information about rattlesnake spatial ecology and translocation in this
video.
Our association with Jude McNally of the Arizona Poison Control Center
goes back nearly 10 years. We have been featured together on several
media events and have worked together to inform the public about
rattlesnakes and the issue of snakebite in general. Collaborating on an
educational program dealing with issues of rattlesnake translocation would
be a natural next step.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Again, information about rattlesnake spatial ecology and
translocation procedures could be easily incorporated into the text of
sign(s). We could also expand this effort to other golf courses, trailheads,
Tiger Rattlesnake Ecology and Management – Goode & Wall 50
parks and other outdoor venues where rattlesnakes are an issue and where
the potential to reach the public is great.
THREAT RESIDENTIAL DEVELOPMENT
GOAL Design residential developments in a way that will minimize impacts to
rattlesnakes and other herpetofauna.
STRATEGY Work directly with developers during the planning process to design
residential developments that take into consideration relevant aspects of
rattlesnake behavior and ecology.
Work with agencies that regulate residential developments to initiate
regulations that are based on relevant aspects of rattlesnake behavior and
ecology.
Provide movement corridors between winter areas (i.e., rock outcrops) and
foraging areas (e.g., washes and bajada areas).
Establish buffers around rock outcrops and washes, and minimize
destruction of rock outcrops during development.
Maintain low-density zoning in residential areas that abut parks, preserves
and other natural areas.
Encourage the Arizona Game and Fish Department to provide guidelines
to agencies that regulate residential developments.
Encourage developers to support research on the land they are developing
that will give them information on what the effects of the development
might be on rattlesnakes.
ACTION We have worked with the Rocking K Development Company to allow us
to gather baseline data on their land that can be compared to post
development data on rattlesnake ecology and behavior.
We are currently working with Rancho Vistoso Partners, LLC at their
Stone Canyon site in the Tortolita Mountains to study the effects of this
development on rattlesnakes and other herpetofauna This study was
funded by the Arizona Game and Fish Department.
We have received the official endorsement of the Pima County Planning
Department on this study, and on the study in the Tortolita Mountains.
Tiger Rattlesnake Ecology and Management – Goode & Wall 51
THREAT GOLF COURSE/RESORT DEVELOPMENT
GOAL Design golf course and resort developments in a way that will minimize
impacts to rattlesnakes and other herpetofauna.
Educate golfers and guests about differences between real and perceived
threats of living in proximity to rattlesnakes.
STRATEGY Work directly with golf course and resort developers during the planning
process to design golf courses and resorts that take into consideration
relevant aspects of rattlesnake behavior and ecology.
Work with agencies that regulate golf course and resort developments to
initiate regulations that are based on relevant aspects of rattlesnake
behavior and ecology.
Provide movement corridors between winter areas (i.e., rock outcrops) and
foraging areas (e.g., washes and bajada areas).
Establish buffers around rock outcrops and washes, and minimize
destruction of rock outcrops during development.
Maintain low-density zoning in residential areas that abut parks, preserves
and other natural areas.
Encourage the use of “desert-style” golf course designs that minimize the
impact on natural areas and systems.
Maintain as much open space as possible in resort development areas to
facilitate the movement of rattlesnakes.
Use native plants in landscaping along golf courses and in development
areas to maintain natural vegetation communities.
Minimize the use of water developments as they attract non-native species
such as bullfrogs and predatory fish.
Ensure that water developments are designed to enable rattlesnakes and
other wildlife to easily escape if they become entrapped.
Encourage the Arizona Game and Fish Department to provide guidelines
to agencies that regulate golf course and resort developments.
Tiger Rattlesnake Ecology and Management – Goode & Wall 52
Encourage developers and golf course designers to support research on the
land they are developing that will give them information on what the
effects of the development might be on rattlesnakes.
Develop an educational brochure to distribute to golfers and recreationists
using golf courses and resorts where rattlesnakes are common.
Develop interpretive signage at golf courses and resorts that include
information about the natural history and ecology of rattlesnakes.
ACTION We have worked with the Rocking K Development Company to allow us
to gather baseline data on their land that can be compared to post
development data on rattlesnake ecology and behavior.
We are currently working with Rancho Vistoso Partners, LLC at their
Stone Canyon site in the Tortolita Mountains to study the effects of this
development on rattlesnakes and other herpetofauna. In particular, we are
studying the effects of the golf course by riding golf cart paths at night and
by implanting rattlesnakes with radiotelemeters that are using the golf
course.
We have received the official endorsement of the Pima County Planning
Department and the City of Tucson Department of Recreation on the study
in the Tortolita Mountains.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Dennis Caldwell, a graphic designed specializing in
herpetofauna, has created and presented examples of signs to the
development supervisor who is in the process of deciding to proceed with
the project.
THREAT ROAD MORTALITY
GOAL Minimize death of rattlesnakes on roads.
STRATEGY Attempt to reduce the number of road that pass through areas where
rattlesnakes are concentrated or through which rattlesnakes must pass,
such as between rock outcrops and washes.
Use signs that inform motorists to use caution in areas where snakes are
known to be abundant.
Tiger Rattlesnake Ecology and Management – Goode & Wall 53
Conduct studies on the effects of roads on rattlesnakes and other
herpetofauna.
ACTION Biologists at Saguaro National Park have been quantifying road mortality
for the past several years and the death toll is extremely high, with an
estimated 40,000 vertebrates per year dying on roads within the Park.
We have suggested that developers at the Stone Canyon site in the
foothills of the Tortolita Mountains place road signs informing residents to
drive with caution to avoid killing snakes and other animals. We are
optimistic that the developers will take our advice when the site becomes
occupied with residents.
THREAT RATTLESNAKE-PET ENCOUNTERS
GOAL Minimize the number of rattlesnake-pet encounters; pets can kill
rattlesnakes and rattlesnakes can either kill pets or result in costly
veterinarian bills.
STRATEGY Develop an educational brochure to distribute to residents living in areas
where rattlesnakes are common that provides guidance on how to make
your house rattlesnake proof.
Encourage residents to keep their pets confined to their yards to minimize
rattlesnake-pet encounters.
Encourage veterinarians to inform their customers about the risks of
rattlesnake-pet encounters.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property. This
brochure contains information about how to avoid rattlesnake-pet
encounters.
ACKNOWLEDGEMENTS
This study would not have been possible without the contributions of numerous people
and organizations: Scott Breeden, Jennifer Treiber, Chris Scott, Cristina Jones, Roger
Repp, Dennis Caldwell, Dale Turner, Ian Cornelius, Taylor Edwards, Melanie Bucci,
Clint Boal, Chris Davis, Brent Sigafus, Ed Kuklinski, Brian Nelson, Ryan Gann, Chris
Tiger Rattlesnake Ecology and Management – Goode & Wall 54
Fatzinger, James Borgmeyer, Dan Bell, Julia Fonseca, Jeff Moorbeck, Jennifer
Moorbeck, Brent Bibles, Dana Kilbourne, Aaron Kellar, Wendy Kramer, Melissa Gray,
Alejandro Diaz, Craig Billington, Jeff Smith, Bill Savary, Jillian Cowles, Scott Jackson,
George Ferguson, Caren Goldberg, Matt Kaplan, Young Cage, Jill Rubio, Bob Jones,
Melanie Florez, Becky Florez, Kimya Mahzad, Linda Burback, Jill Becker, Frans
Kranenburg, Mechelle Meixner, Randy Babb, Jesus Garcia, Allison Titcomb, Daniella
Patterson, Al Patterson, P.J. Bailey, Carol Crowell, Nancy Fahringer, Keve Sankman,
Irma Sankman, Jesse White, Jeff Karthizer, Kim Kronenberg, Ron Lancaster, Sandy
Lebron, Vivian MacKinnon, Pinau Merlin, Pam Anning, Kristen Beaupre, Don de
Young, Jim Jarchow, Stephanie Cameron, John Warnock, Don Swann, Dave Hardy,
Dave Duvall, Peter Cunio, Dave Prival, Phil Rosen, Andy Holycross, Bill Mannan, Bill
Shaw, Karen Galindo, Craig Wistler, Andy Honaman, Chuck Whitney, Roy Averill-
Murray, Natasha Kline, Larry Norris, Jude McNally, Bob Brandner, Susan Basford, Bob
Lineback, Rich Hayes, Lisa Carder, Dave Anning, Bill Dabney, Aracelli Gonzalez, John
Williams, Jay Laughlin, Meg Weesner, Joel Peterson, Shawnee Riplog, and Cecil
Schwalbe. Special thanks go to Andrea Tuijl, and Remi Tuijl-Goode for their patience
and support. Funding sources included: Arizona Game and Fish Department Heritage
Fund, Southwestern Parks and Monuments Association, Tucson Zoological Society, Reid
Park Zoo Teen Volunteers, Denver Zoological Society, National Park Service, Oklahoma
State University, Desert Southwest Cooperative Ecosystem Studies Unit, University of
Arizona, and Saguaro National Park.
LITERATURE CITED
Amaral, A. do. 1929. Notes on Crotalus tigris Kennicott 1859. Bulletin Antivenin
Institute of America. 2:82-85.
Armstrong, B.L., and J.B. Murphy. 1979. The natural history of Mexican rattlesnakes.
University of Kansas Museum of Natural History Special Publications. (5):1-88.
Baird, S.F. 1859. Crotalus tigris Kennicott. Report on the United States and Mexican
Boundary Survey. 2:14.
Beaupre, S.J. 1995. Comparative ecology of the rock rattlesnake, Crotalus lepidus, in
Big Bend National Park. Herpetologica. 51:45-56.
Beaupre, S.J., and D.J. Duvall. 1998. Integrative biology of rattlesnakes: contributions
to biology and evolution. Bioscience. 48:531-538.
Beck, D.D. 1995. Ecology and energetics of three sympatric rattlesnake species in the
Sonoran Desert. Journal of Herpetology. 29:211-223.
Tiger Rattlesnake Ecology and Management – Goode & Wall 55
Campbell, J.A., and W.L. Lamar. 1989. The Venomous Reptiles of Latin America.
Cornell University Press, Ithaca, New York.
Duvall, D., S.J. Arnold, and G.W. Schuett. 1992. Pitviper mating systems: ecological
potential, sexual selection, and microevolution. In, Biology of the Pitvipers. Eds. J.A.
Campbell and E.D. Brodie, Jr. Selva, Tyler, Texas.
Duvall, D., J.K. OíLeile, S.G. Heald, and S.J. Beaupre. 1995. Urban rattlesnake status
and ecology. Final report to Arizona Game and Fish Department (U93032), Phoenix.
Ernst, C.H. 1992. Venomous reptiles of North America. Smithsonian Institution Press,
Washington. 236.
Fowlie, J.A. 1965. The snakes of Arizona. Azul Quinta Press, Fallbrook, California.
Gloyd, H.K. 1937. A herpetological consideration of faunal areas in southern Arizona.
Bulletin of the Chicago Academy of Sciences. 5:131.
Gloyd, H.K. 1940. The rattlesnakes, genera Sistrurus and Crotalus. Chicago Academy
of Sciences Special Publications. 4:1-266.
Goldberg, S.R. 1999. Reproduction in the tiger rattlesnake, Crotalus tigris (Serpentes:
Viperidae). Texas Journal of Science. 51:31-36.
Klauber, L.M. 1931. Crotalus tigris and Crotalus enyo, two little known rattlesnakes of
the southwest. Transactions of the San Diego Society of Natural History. 4:353-370.
Klauber, L.M. 1935. Notes on herpetological collecting. San Diego Natural History
Society. Collecting Leaflet No. 1.
Klauber, L.M. 1956. Rattlesnakes: their habits, life histories and influence on mankind.
1st Edition. University of California Press, Berkeley, California.
Klauber, L.M. 1972. Rattlesnakes: their habits, life histories and influence on mankind.
2nd Edition. University of California Press, Berkeley, California.
Lowe, C.H., C.R. Schwalbe, and T.B. Johnson. 1986. The venomous reptiles of Arizona.
Arizona Game and Fish Department, Phoenix, Arizona.
McNally, J, and T. Hare. 1996. Evaluation of a rattlesnake relocation program. Final
report submitted to the Arizona Game and Fish Department (U93009), Phoenix.
Tiger Rattlesnake Ecology and Management – Goode & Wall 56
Nowak, E.M., and C. van Riper, III. 1999. Effects and effectiveness of rattlesnake
relocation at Montezuma Castle National Monument. Technical Report
#USGSFRESC/COPL/1999/17. USGS Forest and Rangeland Ecosystem Science Center,
Biological Resources Division, Colorado Plateau Field Station. Northern Arizona
University. Flagstaff, Arizona.
Prival, D.B., M.J. Goode, D.E. Swann, and C.R. Schwalbe, M.J. Schroff, and R.J. Steidl.
1999. A comparative study of hunted vs. unhunted populations of the twin-spotted
rattlesnake. Final report to Arizona Game and Fish Department, Phoenix.
Prival, D. B., and C. R. Schawalbe. 2000. Conservation and management of
commercially valuable snake species at Chiricahua National Monument. Final report to
the Southwestern Parks and Monuments Association.
Reinert, H. K., and D. Cundall. 1982. An improved surgical implantation method for
radio-tracking snakes. Copeia. 3:702-705.
Reinert, H.K., and R.R. Rupert. 1999. Impacts of translocation on behavior and survival
of timber rattlesnakes, Crotalus horridus. Journal of Herpetology. 33:45-61.
Rocking K Specific Plan. 1991. Pima County, Arizona.
Rocking K Specific Plan (Amended). 1996. Pima County, Arizona.
Rubio, M. 1998. Rattlesnake: portrait of a predator. Smithsonian Institution Press,
Washington and London.
Schuett, G.W., and J.C. Gillingham. 1988. Courtship and mating of the copperhead,
Agkistrodon contortrix. Copeia. 1986:807-811.
Schuett, G.W. 1992. Is long-term sperm storage an important component of the
reproductive biology of temperate pitvipers? In, Biology of the Pitvipers. Eds. J.A.
Shine, R. 1978. Sexual size dimorphism and male combat in snakes. Oecologia.
33:269-277.
Turner, R. M., and D. E. Brown. 1982. Sonoran desertscrub vegetation. Desert-Plants.
4:181-219.
Wright, A.H., and A.A. Wright. 1957. Handbook of snakes of the United States and
Canada. Comstock Publishing Company, Ithaca, New York.
Tiger Rattlesnake Ecology and Management – Goode & Wall 57
APPENDIX A
Raw data from 169 tiger rattlesnakes captured at three sites in and adjacent to Saguaro
National Park, and by Rural Metro Fire Department personnel in the foothills of the Santa
Catalina Mountains. LR = Loop Road, TVR = Tanque Verde Ridge, A = adult, Repro =
reproductive status, NG = not gravid, G = gravid, NS = no semen present, S = semen
present, SVL = snout-vent length, TL = tail length, HW = head width, HL = head length,
RS = number of rattle segments, RL = rattle length, RB = rattle broken, Y = yes, and N =
no. All measurements are in millimeters except mass, which is in grams.
1997
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
08/04/97 LR F A NG 670 51 175 17 26 9 44 Y
08/06/97 LR F A G 521 29 175 21 19 4 24 N
08/07/97 TVR F A NG 592 43 259 20 26 8 40 Y
08/10/97 LR M A NS 709 74 471 23 34 10 51 Y
08/12/97 TVR M A NS 680 73 283 20 29 7 36 Y
08/12/97 TVR M A NS 667 64 292 21 29 6 33 Y
08/13/97 TVR M A NS 778 71 380 7 35 Y
08/17/97 LR M A S 713 73 369 23 30 7 18 Y
08/26/97 TVR F A NG 636 45 186 21 28 8 35 Y
08/26/97 LR M A NS 635 72 316 20 29 8 38 Y
08/26/97 LR M A NS 712 46 214 22 30 8 29 Y
08/26/97 LR M A S 656 66 346 28 7 29 Y
08/26/97 LR M A S 673 69 310 31 8 38 Y
08/27/97 TVR F A NG 637 45 261 21 25 7 29 Y
08/27/97 TVR F A NG 600 46 291 21 30 7 30 Y
08/27/97 LR M A NS 730 73 337 22 32 10 49 Y
08/27/97 TVR M A S 650 65 261 20 31 5 27 Y
09/02/97 TVR F A NG 688 47 226 20 27 8 33 Y
09/05/97 TVR M A S 680 66 325 20 31 9 43 Y
09/12/97 TVR F A NG 627 45 251 18 26 7 38 N
09/27/97 TVR M A NS 694 65 317 19 29 9 Y
10/02/97 TVR M A S 687 71 355 26 28 7 32 Y
10/15/97 TVR M A NS 647 58 236 22 29 6 30 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 58
1998
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
05/23/98 TVR M A NS 694 63 348 21 29 7 32 Y
07/03/98 TVR F A NG 647 43 275 19 27 8 35 Y
07/08/98 TVR M A NS 612 43 263 26 17 9 43 Y
07/17/98 LR M A NS 741 72 357 21 30 9 40 Y
08/02/98 LR F A NG 659 50 231 19 27 10 45 Y
08/02/98 LR M A S 728 67 356 18 28 9 41 Y
08/02/98 LR M A S 629 56 257 20 26 7 Y
08/09/98 RK M A S 699 70 388 22 29 10 49 Y
08/10/98 LR M A NS 687 74 400 23 26 9 44 Y
08/12/98 TVR M A S 627 58 299 22 27 8 32 Y
08/12/98 LR M A S 732 65 496 23 28 6 30 Y
08/12/98 TVR M A NS 738 67 433 22 28 9 49 Y
08/12/98 TVR M A S 693 68 401 22 29 7 44 Y
08/20/98 LR M A S 697 63 357 23 30 12 51 Y
08/20/98 LR M A S 602 60 260 21 27 7 35 N
08/21/98 TVR M A NS 553 51 185 19 25 6 31 N
08/23/98 LR M A S 772 69 512 21 29 10 43 Y
08/25/98 TVR F A NG 650 51 264 20 27 9 40 Y
08/27/98 LR F A G 610 42 236 21 30 10 43 Y
08/27/98 LR M A NS 602 67 395 22 30 7 35 Y
08/30/98 TVR F A NG 635 45 243 20 29 8 34 Y
08/31/98 TVR F A NG 658 42 326 19 28 10 45 Y
09/02/98 LR M A S 636 66 291 20 26 7 31 Y
09/04/98 RMFD M A S 730 70 474 23 28 6 34 Y
09/04/98 RMFD F N NG 252 18 18 13 17 1
09/11/98 TVR F A NG 564 35 158 17 24 3 20 Y
09/12/98 LR M A S 725 65 390 19 28 10 49 Y
09/21/98 LR M A S 729 71 400 18 28 10 50 Y
10/21/98 RMFD M A S 659 56 281 19 25 10 46 Y
10/21/98 RMFD F A 577 46 239 19 23 7 40 N
10/21/98 RMFD F A G 669 46 369 20 25 10 31 Y
10/24/98 TVR M A NS 601 55 215 19 23 7 36 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 59
1999
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
05/27/99 TVR M A 682 60 285 19 27 8 38
05/01/99 LR F A G 597 43 362 6 Y
06/30/99 RMFD M A 700 64 360 33
07/03/99 RMFD M A 713 67 384 43 Y
07/26/99 RK M A NS 682 66 305 21 27 9 45 Y
07/30/99 RK F A NG 634 50 148 16 25 8 30 Y
08/04/99 TVR F A NG 537 41 156 17 22 5 25 N
07/28/99 RMFD M A S 767 73 469 24 30 4 25 Y
07/26/99 RMFD F A 511 41 156 18 23 5 24 N
07/26/99 RMFD F A 534 39 160 19 24 5 24 N
08/02/99 RMFD F A NG 584 36 278 18 27 8 33 Y
08/02/99 RMFD M A S 535 58 161 18 25 5 23 N
07/15/99 RMFD M A S 636 55 165 17 25 5 24 N
08/31/99 RK M A S 684 66 288 20 28 11 50 Y
08/30/99 TVR F J NG 511 38 113 17 25 5 25 N
09/01/99 TVR M A S 712 66 345 21 31 10 50 Y
09/02/99 RK M A S 739 71 385 21 30 10 51 Y
09/04/99 RK M A NS 636 74 378 22 29 9 46 Y
09/05/99 RK M A NS 761 70 426 24 31 10 46 Y
09/05/99 RK M A S 638 59 246 19 27 5 27 Y
09/05/99 RK F A NG 596 41 179 19 26 7 32 Y
09/05/99 RK M A NS 686 68 234 22 29 6 30 Y
09/06/99 RK M A S 753 69 415 24 33 10 49 Y
09/14/99 RK F A NG 619 36 150 16 25 6 27 Y
09/14/99 TVR M A S 711 64 455 26 29 8 39 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 60
2000
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
06/05/00 RK M J NS 394 34 46 15 22 1 14 N
06/05/00 RK M J NS 561 52 134 22 27 5 Y
06/13/00 LR M A 692 68 340 21 28 12 49 Y
06/27/00 RK M A NS 649 64 265 20 26 9 40 Y
06/29/00 RK M J 357 37 53 14 20 3 18 Y
06/29/00 LR M A 531 44 158 17 24 5 25 N
07/01/00 TVR F A NG 681 51 249 22 29 10 40 Y
07/02/00 TVR M A NS 632 55 195 17 25 6 27 Y
07/05/00 RK M A NS 689 67 308 21 30 10 48 Y
07/10/00 RK M A NS 712 63 298 20 29 9 39 Y
07/11/00 RK F A NG 667 48 252 21 28 9 42 Y
07/11/00 RK M A NS 716 62 383 21 30 9 46 Y
07/11/00 RK M A S 658 59 301 22 29 10 51 Y
07/13/00 RK M J S 492 48 95 18 24 5 24 Y
07/14/00 LR M A S 737 73 434 23 29 7 35 Y
07/14/00 LR F J NG 477 35 102 20 25 4 19 N
07/14/00 LR M A NS 699 67 336 21 29 10 44 Y
07/15/00 LR M A S 676 63 297 21 29 9 41 N
07/15/00 LR M A NS 749 62 315 23 30 10 43 Y
07/17/00 RK F A NG 569 39 183 19 26 6 29 N
07/17/00 RK F A NG 614 44 141 19 26 6 20 Y
07/17/00 RK M A NS 661 64 275 21 28 21 28 Y
07/17/00 RK M N NS 283 24 20 14 18 1 8.1 N
07/19/00 RK F N NG 286 21 19 13 18 1 9 N
07/20/00 TVR F A NG 624 42 266 24 28 11 47 Y
07/22/00 RK M A S 690 65 284 20 27 8 36 Y
07/24/00 RK F A NG 669 46 196 21 28 5 26 Y
07/24/00 RK M A NS 610 63 227 10 42 Y
07/24/00 RK M A S 684 61 332 19 29 9 37 Y
07/25/00 RK F A G 630 40 208 23 30 10 45 Y
07/25/00 RK F A G 539 38 154 19 25 6 30 N
07/27/00 RK M A S 704 70 418 25 31 9 46 Y
07/27/00 RK M A S 739 65 320 23 28 13 56
07/28/00 RK F A NG 683 44 183 21 28 9 42 Y
07/28/00 RK M A NS 639 62 260 23 29 8 34
08/01/00 RK M A S 542 51 147 19 25 3 18 Y
08/08/00 TVR M A S 653 57 270 21 28 7 34 Y
08/10/00 RK F A NS 541 41 182 18 24 6 26 N
08/10/00 RK F N NG 294 25 20.5 13 19 1 8.7 N
08/12/00 TVR M A S 562 53 142 25 27 6 30 N
09/02/00 RK M A S 560 59 145 19 24 6 29 N
Tiger Rattlesnake Ecology and Management – Goode & Wall 61
2000 (con’t.)
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
09/09/00 RK M A S 605 58 209 18 26 6 31 N
09/20/00 RK M J S 448 39 73 16 23 4 20 N
09/20/00 RK F J NG 426 35 60 14 20 4 19 N
09/25/00 RK M J S 580 56 129 17 25 5 27 N
09/28/00 TVR M A S 742 68 354 21 28 11 42 Y
09/30/00 RK M A S 590 58 154 18 26 8 33 Y
10/01/00 RK M A S 676 68 345 21 29 9 46 Y
10/25/00 RMFD M A S 666 68 398 23 29 8 37 Y
11/10/00 TVR M A NS 538 49 114 16 24 5 24 N
2001
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
04/28/01 RK F J NG 180 29 31 18 17 1 9 N
05/24/01 RK F J NG 550 38 140 18 25 8 41 N
05/27/01 RK F J NG 356 26 47 17 20 2 12 N
06/10/01 LR M J NS 544 49 176 22 26 6 29 N
06/17/01 RK F J NG 511 34 95 18 23 5 27 N
06/18/01 RK M J NS 327 27 24 14 18 2 13 N
07/04/01 TVR M A S 554 56 146 17 26 6 28 N
07/09/01 LR F A G 646 44 278 23 28 10 42 Y
07/09/01 LR M A NS 618 68 237 19 26 6 25 Y
07/11/01 RK M A NS 731 70 421 25 31 9 43 Y
07/11/01 RK M J NS 645 51 164 19 25 5 25 N
07/13/01 RK M A NS 553 55 180 21 27 5 24 Y
07/15/01 LR F A G 599 41 225 20 28 6 31 Y
07/16/01 LR M A NS 772 68 436 21 29 3 15 Y
07/16/01 RMFD M A NS 607 52 177 18 25 7 33 Y
07/16/01 RMFD M A NS 651 60 215 20 28 7 32 Y
07/23/01 LR M A NS 607 57 196 17 26 7 34 N
07/23/01 LR F A NG 599 40 219 18 26 7 36 N
07/24/01 LR M A NS 696 64 313 19 28 7 35 Y
07/30/01 RK M A S 646 66 247 22 28 9 42 Y
07/30/01 RK F A G 554 39 167 19 23 7 32 Y
08/04/01 RMFD M A NS 716 65 354 22 30 5 23 Y
08/05/01 RMFD M A NS 733 65 491 22 27 11 55 Y
08/06/01 RK M A NS 689 64 285 18 27 10 47 Y
08/06/01 RK M A NS 703 69 383 22 26 8 38 Y
08/08/01 RK M J S 496 43 86 19 22 4 22 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 62
2001 (con’t.)
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
08/09/01 RK M A NS 690 62 323 20 28 12 50 Y
08/09/01 LR M A NS 689 67 306 20 29 6 30 Y
08/13/01 RK M A NS 670 62 287 21 27 6 27 Y
08/13/01 RMFD M A S 637 54 259 19 28 6 33 N
08/14/01 RMFD M A NS 708 68 389 21 28 3 19 Y
08/16/01 RK M J NS 545 59 157 17 25 7 33 Y
08/25/01 RK M A S 578 54 184 18 25 7 28 Y
08/30/01 RMFD M A Y
09/07/01 RK M J S 502 52 129 17 21 5 24 N
09/08/01 RMFD M A S 707 66 22 29 8 32 Y
09/23/01 RK F A G 546 37 190 17 26 6 29 N
09/22/01 LR F A NG 578 45 228 19 28 7 29 Y

Click tabs to swap between content that is broken into logical sections.

Copyright to this resource is held by the creating agency and is provided here for educational purposes only. It may not be downloaded, reproduced or distributed in any format without written permission of the creating agency. Any attempt to circumvent the access controls placed on this file is a violation of United States and international copyright laws, and is subject to criminal prosecution.

Tiger Rattlesnake Ecology and Management
(Heritage Grant Number U97015 - Urban Rattlesnakes: A Management Plan)
FINAL REPORT
November 4, 2002
Matthew J. Goode and Michael D. Wall
School of Renewable Natural Resources
University of Arizona
Tucson, AZ 85721
Submitted to the Arizona Game and Fish Department
Heritage Urban Wildlife Program
Recommended Citation
Goode, M.J. and M.D. Wall. 2002. Tiger rattlesnake ecology and management.
Nongame and Endangered Wildlife Program Heritage Report. Arizona Game and Fish
Department, Phoenix, Arizona.
Disclaimer
The findings, opinions, and recommendations in this report are those of the investigators
who have received partial or full funding from Arizona Game and Fish Department
Heritage Fund. The findings, opinions, and recommendations do not necessarily reflect
those of the Arizona Game and Fish Commission of the Department, or necessarily
represent official Department policy or management practice. For further information,
please contact the Arizona Game and Fish Department.
Tiger Rattlesnake Ecology and Management – Goode & Wall i
Table of Contents
INTRODUCTION ...............................................................................................................1
METHODS.........................................................................................................................2
Study Area ...............................................................................................................2
Search Effort ............................................................................................................4
Road Cruising ..........................................................................................................4
Capture, Marking, Handling ....................................................................................4
Morphology..............................................................................................................5
Demography.............................................................................................................5
Reproduction............................................................................................................6
Radio Telemetry.......................................................................................................6
Spatial Ecology ........................................................................................................7
Growth .....................................................................................................................7
Feeding and Diet ......................................................................................................8
Habitat Analyses ......................................................................................................8
Small Mammal Trapping .........................................................................................9
Lizard Abundance Index........................................................................................10
Amphibian and Reptile Observations ....................................................................10
Data Analyses ........................................................................................................10
RESULTS AND DISCUSSION........................................................................................10
Search Effort ..........................................................................................................10
Road Cruising ........................................................................................................11
Tiger Rattlesnake Ecology and Management – Goode & Wall ii
Capture-Recapture .................................................................................................14
Demography...........................................................................................................15
Morphology............................................................................................................17
Reproduction..........................................................................................................19
Growth ...................................................................................................................26
Spatial Ecology ......................................................................................................29
Feeding and Diet ....................................................................................................31
Habitat....................................................................................................................37
Small Mammal Trapping .......................................................................................40
Lizard Abundance Index........................................................................................41
MANAGEMENT IMPLICATIONS .................................................................................43
A MANAGEMENT PLAN FOR URBAN RATTLESNAKES........................................47
Direct Killing of “Nuisance” Rattlesnakes ............................................................47
Translocation of “Nuisance” Rattlesnakes.............................................................48
Residential Development.......................................................................................50
Golf Course/Resort Development..........................................................................51
Road Mortality.......................................................................................................52
Rattlesnake – Pet Encounters.................................................................................53
ACKNOWLEDGEMENTS...............................................................................................53
LITERATURE CITED......................................................................................................54
APPENDIX A....................................................................................................................57
Tiger Rattlesnake Ecology and Management – Goode & Wall iii
Tables
1. Tiger rattlesnakes captured per unit effort ...................................................................11
2. Tiger rattlesnakes encountered while road cruising.....................................................12
3. Amphibian and reptile species observed while road cruising......................................12
4. Tiger rattlesnake morphometric data ...........................................................................18
5. Tiger rattlesnake body and head size data ...................................................................19
6. Date ranges of tiger rattlesnake reproductive activity .................................................21
7. Average litter size of Arizona rattlesnakes ..................................................................23
8. Morphological data for tiger rattlesnake litter .............................................................24
9. Mean SVL of gravid tiger rattlesnakes ........................................................................24
10. Summary of tiger rattlesnake movement and home range data...................................32
11. Relative abundance, by site, of lizards.........................................................................36
12. Tiger rattlesnake microhabitat data..............................................................................38
13. Small mammals trapped at Tanque Verde Ridge ........................................................40
14. Incidental reptiles and amphibians encountered ..........................................................41
15. Relative abundance of prey lizards by season .............................................................42
16. Relative abundance of prey lizards by habitat type .....................................................43
Tiger Rattlesnake Ecology and Management – Goode & Wall iv
Figures
1. Photograph of adult male tiger rattlesnake ....................................................................2
2. Map of Saguaro National Park and surrounding urban areas ........................................3
3. Aerial photograph of tiger rattlesnakes encountered while road cruising ...................13
4. Tiger rattlesnakes by site .............................................................................................14
5. Sex by site ....................................................................................................................15
6. Age class by site...........................................................................................................16
7. Size class distribution ..................................................................................................16
8. Adult size by site..........................................................................................................20
9. Ratio of tail length to SVL by sex ...............................................................................20
10. Semen present by season .............................................................................................21
11. Reproductive activity by year ......................................................................................22
12. Proportion giving birth.................................................................................................23
13. Rainfall by season and year .........................................................................................26
14. Growth by season.........................................................................................................27
15. Growth by year ............................................................................................................27
16. Growth per year of radio and non-radioed snakes .......................................................28
17. Aerial photograph of all tiger rattlesnake locations.....................................................29
18. Minimum convex polygon home ranges for selected tiger rattlesnakes......................30
19. Minimum convex polygon home range by season ......................................................33
20. Minimum convex polygon home range by gender ......................................................34
21. Tiger rattlesnake diet....................................................................................................35
Tiger Rattlesnake Ecology and Management – Goode & Wall v
22. Percent bolus by season ...............................................................................................35
23. Diet by sex ...................................................................................................................36
24. Diet by site ...................................................................................................................37
25. Seasonal variation in habitat selection.........................................................................39
26. Aerial photograph of transboundary movements at Tanque Verde Ridge ..................44
27. Aerial photograph of transboundary movements at Rocking K ..................................45
Tiger Rattlesnake Ecology and Management – Goode & Wall 1
INTRODUCTION
Prior to this study, the tiger rattlesnake (Crotalus tigris) was one of the least studied
rattlesnake species in the United States (Ernst 1992). Much of what was known about
tiger rattlesnakes came from a small number of field observations and museum
specimens, consisting mainly of physical descriptions, scale counts and information on
their distribution (Baird 1859, Amaral 1929, Klauber 1931, Gloyd 1940, Campbell &
LaMar 1989). Knowledge of the natural history of this secretive species was largely
anecdotal (Gloyd 1937, Fowlie 1965, Klauber 1972; Armstrong & Murphy 1979; Lowe,
et al. 1986). Basic ecological and physiological data were virtually nonexistent until
Beck (1995) published data on a small sample (n = 3) of male tiger rattlesnakes that he
studied using radiotelemetry.
Duvall et al. (1995) tracked 6 tiger rattlesnakes using radiotelemetry, but their objective
was to document the presence of rattlesnakes in isolated preserves throughout the
Phoenix, Arizona metropolitan area, and to assess the degree to which these snakes were
using surrounding urbanized areas. Because they only located radio-equipped snakes a
total of 32 times, they learned a limited amount about tiger rattlesnake biology.
However, they recognized the need for a more detailed study of rattlesnakes living near
urbanized areas. In this vein, McNally & Hare (1996) radiotracked several rattlesnakes,
one of which was a male tiger rattlesnake, to determine movement patterns of
rattlesnakes that were translocated by the Rural Metro Fire Department (RMFD) in
Tucson. These snakes appeared to exhibit aberrant movement patterns, and little was
learned about the natural behavior of tiger rattlesnakes.
Herpetologists have recognized the need for a detailed study of C. tigris for decades
(Gloyd 1940, Klauber 1956, Ernst 1992, Rubio 1998). Therefore, our goal was to expand
our knowledge of tiger rattlesnakes by intensively studying a large sample of radiotagged
snakes. In this report we present the results of the first five years (1997 – 2001) of an
ongoing, long-term study of tiger rattlesnakes at an urban/wildland interface near Tucson,
Arizona. Specifically, we studied tiger rattlesnakes at Saguaro National Park (SNP), and
at two sites on private land immediately adjacent to the park: a low-density residential
area, and the future site of a large urban development. We also obtained information
from tiger rattlesnakes captured by RMFD personnel.
In addition to studying tiger rattlesnake natural history and ecology, our objective was to
use this knowledge to develop more effective management strategies for rattlesnakes in
general. In particular, there is a need to manage rattlesnakes that live along the
boundaries of parks and preserves and that move into adjacent urbanized areas. Tiger
rattlesnakes are a good choice for investigating the effects of urbanization on rattlesnakes
for several reasons. The range of the tiger rattlesnake in Arizona is centered around
Phoenix and Tucson, two rapidly expanding urban areas surrounded by wildlands. Tiger
rattlesnakes prefer rocky desert uplands; these upland areas are also considered prime real
estate, and they are being developed at an alarming rate. An estimated 3,000-5,000
Tiger Rattlesnake Ecology and Management – Goode & Wall 2
rattlesnakes, including tiger rattlesnakes, are removed by RMFD every year from the
yards of residents living in Tucson (McNally 1995, G. Good, RMFD, pers. comm.). In
Phoenix, rattlesnake removal services are also provided by the fire department and by
members of the Arizona Herpetological Association, an amphibian and reptile
enthusiasts’ club (J. Feldner, pers. comm.). Rattlesnake management is also an issue at
SNP. One of the biggest concerns facing the park is what to do about wildlife that move
in and out of the park, especially as the city of Tucson continues to expand, further
surrounding the park (Goode 2001, SNP Resource Management Plan). This is also true
for other urban/wildland interfaces in the Tucson and Phoenix areas, including US Forest
Service lands in the Santa Catalina and Rincon Mountains, Pima County Park lands in the
Tucson and Tortolita Mountains, municipal lands comprising the Phoenix mountain
parks, and a variety of other land ownership entities throughout Pima and Maricopa
counties. Our goal was to use the results of this research to address these growth-related
concerns.
METHODS
Study Area
We studied tiger rattlesnakes (Figure 1) at three sites in the Rincon Mountain District of
SNP (Figure 2). The Tanque Verde Ridge (TVR) site is located in the extreme southwest
Figure 1. Adult male tiger rattlesnake (Crotalus tigris). Photograph by Chris Scott.
Tiger Rattlesnake Ecology and Management – Goode & Wall 3
corner of the park. This site is bordered by Old Spanish Trail, a busy commuter road that
runs along the west boundary of the park, and a low-density housing area immediately
adjacent to the south boundary. The Rocking K (RK) site is situated along the park’s
south boundary approximately 4 km east of TVR. This area is the future site of the
Rocking K development, a large scale project consisting of a resort and golf courses,
approximately 5,000 dwelling units, and small commercial zones. The Loop Road (LR),
the only road in the park used by visitors, begins and ends at the Visitor Center and it alos
provides access to the Javelina Picnic Grounds.
Figure 2. Map of Saguaro National Park and surrounding urban areas, showing all three
study areas. LR = Loop Road; TVR = Tanque Verde Ridge; RK = Rocking K Ranch.
Figure 2. Map of Saguaro National Park and surrounding urban areas, showing all three
study areas. LR = Loop Road; TVR = Tanque Verde Ridge; RK = Rocking K Ranch.
All three sites are characterized by steep rocky slopes, ridges with exposed bedrock, and
bajadas dissected by numerous washes, some of which are characterized by relatively
well developed soil terraces and xeroriparian vegetation. Vegetation is typical of
Sonoran Desertscrub, Arizona Upland Subdivision (Turner & Brown 1982). Common
plants include saguaro (Carnegia gigantea), foothill paloverde (Cercidium
microphyllum), brittlebush (Encelia farinosa), prickly pear and cholla (Opuntia spp.), and
velvet mesquite (Prosopis velutina). Elevation at all three sites ranges from
approximately 900 – 1100 m (2,940 – 3,700 ft). We also obtained information from tiger
rattlesnakes, which were removed from residences by RMFD personnel. These snakes
originated from throughout the foothills of the Santa Catalina Mountains, approximately
10-25 km northwest of our main study areas at SNP.
LR
TVR
RK
KK
Tiger Rattlesnake Ecology and Management – Goode & Wall 4
Search Effort
When we began the study in August 1997, with the aid of numerous volunteers, we
conducted walking searches in an attempt to obtain tiger rattlesnakes for radiotelemeter
implants. In 1998, we turned our attention to radiotracking the snakes we captured and
implanted in 1997. We continued to conduct a limited number of searches in 1998,
acquiring several more snakes for implantation. In 1999, we began studying tiger
rattlesnakes at RK, where we conducted several searches in an attempt to acquire snakes
for implantation. In 2000, we did not conduct any walking searches specifically for tiger
rattlesnakes; however, we obtained numerous snakes from tortoise researchers who
captured them while conducting distance sampling at RK. In 2001, we conducted one
walking search at TVR, and we received several more snakes from tortoise researchers
who were continuing to conduct distance sampling at RK.
We also acquired snakes while radiotracking, including those found in association with
our radiotagged snakes, which occurred on several occasions during the mating season.
Because the amount of time searching for snakes while radiotracking is less than when
conducting snake hunts, we compared the number of snakes captured during each activity
to arrive at an estimate of total search effort. We estimated search effort of tortoise
researchers to be equal to search effort while conducting snake hunts, because it is likely
that tortoise researchers missed few tiger rattlesnakes while searching (D. Swann, R.
Averill-Murray, pers. comm.).
Road Cruising
We spent a significant amount of time road cruising the LR, where we acquired numerous
snakes. The LR is nine miles in length, winding through relatively pristine desert. The
LR begins at approximately 1000 m, and reaches a maximum elevation of approximately
1200 m. We found tiger rattlesnakes along a 3.7 mile stretch of the LR, where the road
winds through rocky foothill areas on the west side of Tanque Verde Ridge. We did not
encounter any tiger rattlesnakes in lower elevation creosote flats.
Capture, Marking and Handling
We captured snakes using 24” tongs (Whitney, Inc). We transported snakes in cloth bags
to the senior author’s residence for processing (e.g., measured, sexed, palpated). We
permanently marked each snake by injecting a passive integrated transponder (PIT tag)
under the skin. These tiny electronic devices are about the size of a grain of rice. PIT
tags enabled us to identify individuals by passing a PIT tag reader (Destron-Fearing Co.),
which displays a 10-digit alphanumeric code, over the snake’s body. We coded digits 0-9
with different paint colors, which were then used to paint the first three proximal rattle
segments of the rattle based on the last three numeric digits of the alphanumeric code.
This gave each snake a unique rattle paint code, making it unnecessary to recapture
snakes observed in the field if the paint colors were visible. In some cases, when snakes
Tiger Rattlesnake Ecology and Management – Goode & Wall 5
were recaptured for growth measurements or to replace their radiotelemeter, we repainted
the rattle if necessary. In general, paint marks were quite resilient; however, over time
they will either wear off or the rattle segments containing the paint mark will break off.
Therefore, they are not considered permanent. The paint mark also allowed us to
quantify the number of times a rattlesnake shed its skin.
We used plastic tubes (JB Specialties, Inc.), a hook (Rattlesnake Museum, Albequerque,
NM) and a “squeezebox” (a wooden box lined with foam padding) to safely handle
rattlesnakes during capture and processing. Our experience handling venomous snakes
minimized risk to both the snakes and ourselves. Snakes were released within 3-48
hours, depending on whether or not they were chosen for a radiotelemeter implant.
Morphology
We recorded snout-vent length (SVL), tail length, mass, head width and head length for
all snakes captured. We measured SVL using a squeezebox. We traced the total length
of the snake (minus the rattle) twice on the plexiglass cover of the squeezebox. We
measured the trace twice to help insure accuracy. If measurements differed by greater
than 1% of the total length, then we measured again until we obtained two measurements
that were within 1% of each other. We also traced the outline of the head to get length
and width measurements.
We tubed snakes in order to measure tail length, which we subtracted from the total
length to arrive at SVL. We weighed snakes in a cloth bag and then subtracted the mass
of the empty bag to determine the mass of the snake. We calculated the mass of the
snake per unit body length by dividing the mass by SVL. This produces a body condition
index (BCI), which can be compared among individuals. We also calculated the ratio of
tail length to body length to facilitate sexing, as female tails are shorter than males’
relative to their body length.
Demography
We sexed all snakes captured and classified each one into one of three age classes: adult,
subadult, and neonate. For a female snake to be classified as an adult, it had to exceed
the minimum size at which we found gravid individuals. For a male snake to classified
as an adult, it had to exceed the minimum size at which males have been found to be
reproductively mature (Goldberg 1999). We distinguished neonates from subadults
based on their small size and by the presence of a rattle consisting of only one segment
called the button, indicating that the snake had only shed once, approximately one week
after birth.
Tiger Rattlesnake Ecology and Management – Goode & Wall 6
Reproduction
Each time we tracked a snake, we recorded whether or not it was with a conspecific of
the opposite sex. We classified each conspecific pairing into one of three categories:
accompaniment, courtship, or copulation. We defined accompaniment as a male and
female located within 1 m of each other. Courtship consisted of obvious behaviors such
as chin-pressing and tail-searching (Klauber 1972). Copulation, which can be difficult to
discern from courtship (Schuett & Gillingham 1988), was only scored if we were certain
that intromission had occurred, as evidenced by a distended cloaca of the female, or the
female dragging the male around while in a copulatory lock.
We palpated female snakes to assess reproductive condition. Small, hard ovarian
follicles were easily palpated on females in the late summer and fall. Larger, softer
yolking follicles were evident in spring, and embryos could be detected in summer.
Although experience has enabled us to be fairly accurate in our assessment of female
reproductive condition, there is some margin for error, especially in determining the exact
number of ova or embryos.
Although we tracked several radiotagged females, which undoubtedly gave birth, we
were unable to obtain any data on their litters because we were unsuccessful in finding
the neonates. On several occasions, we had females, which were obviously gravid, make
movements after a long period of quiessence. Upon locating the female, it was obvious
she had given birth, however, we were unable to find her offspring when we returned to
her previous location.
In an attempt to assess male reproductive condition, we recorded the presence of semen
expressed from the hemipenal shafts. We have not yet determined if semen contains live
sperm; however, a reptile and amphibian veterinarian (J. Jarchow, pers. comm.) indicated
that live sperm are almost certainly present in the semen of mature males during the
mating season.
Radiotelemetry
We surgically implanted temperature-sensing radiotelemeters (Holohil, Ltd., Model SR2)
into 35 tiger rattlesnakes. Radiotelemeters were designed to last two years;
unfortunately, more than half failed prematurely due to faulty batteries. Therefore, we
were unable to track the snakes we captured in 1997-1998 as long as originally intended.
In a few cases, individuals were only tracked a few times before their radiotelemeter
failed. Despite these problems, we were still able to follow several individuals for
multiple years, and we were able to obtain a large dataset on numerous individuals.
We only implanted snakes if the mass of the radiotelemeter (11.6 g) was 5% or less of the
snake’s mass. This resulted in a minimum mass of 232 g to be eligible for an implant,
although a snake also had to be large enough in diameter (determined by visual
Tiger Rattlesnake Ecology and Management – Goode & Wall 7
inspection and based on experience) to receive an implant. Occasionally, a snake met the
minimum mass criteria but was rejected because it appeared to be too thin or unhealthy.
We anesthetized snakes using Isoflurane (Abbott Laboratories), an inhalant, which is
highly soluble in tissue and allows for precise dosing. Using a sterile procedure
(modified from Reinert & Cundall 1982), we implanted transmitters into the peritoneum
(i.e., gut cavity), with the antennae placed under the skin and stretched toward the head to
increase the range of signal detection. Several snakes received multiple implants. No
snakes died or showed any obvious ill effects of implantation.
Spatial Ecology
We used either a Trimble (Trimble, Inc.) or Garmin E-Map (Garmin, Inc.) global
positioning system (GPS) receiver to record snake locations. We post-processed
locations recorded with the Trimble receiver using Pathfinder software (Trimble, Inc.) to
obtain 1-3 m accuracy. We used base station files obtained from the US Forest Service
office at Tucson, which was approximately 15 miles from our study area, for differential
correction. Locations recorded with the Garmin receiver were not post-processed.
However, these locations were accurate to within 4-7 m because they were obtained after
GPS signals were no longer being scrambled by the government. All GPS data were
imported into ArcView (ESRI, Inc.) for
display and spatial analyses using the Animal Movement Analysis extension (obtained
online from Alaska Biological Science Center, USGS-Biological Resources Division).
We used a variety of parameters to characterize tiger rattlesnake movement patterns,
including total distance moved, mean distance moved per day, mean distance moved per
movement bout, maximum distance moved, and whether or not the snake was moving
when located. To characterize home ranges, we estimated their size using the minimum
convex polygon (MCP) technique and the 95% active kernal technique. We estimated
core activity areas using the 50% isopleth generated by the active kernal technique. This
area contains half of all the locations for a given snake. We examined annual and
seasonal differences in movement patterns and home range size and use when sample
sizes permitted.
Growth
We used morphological data and information on shedding frequency to examine growth.
We attempted to recapture radiotagged snakes upon emergence from winter dens in the
spring and again before they reentered their dens in the fall in order to remeasure them.
By catching snakes just before and just after they overwintered, we were able to examine
growth rates during the active season and determine the effects of hibernation on growth
and mass. We also compared the growth of radiotelemetered snakes with data from non-radiotelemetered
snakes, which were recaptured opportunistically. By comparing
radiotelemetered snakes with non-radiotelemetered snakes, we were able to indirectly
examine the effects, if any, that implants may be having on snakes.
Tiger Rattlesnake Ecology and Management – Goode & Wall 8
Feeding and Diet
We obained information on tiger rattlesnake diet through analyses of fecal matter, which
we obtained by forcing feces out of the hind gut. Fecal samples were frozen and later
placed in water to thaw and to dissolve feces into identifiable prey remains. Prey remains
consisted of hair, claws, bones, teeth, feathers and scales. We were able to identify prey
remains to class level in all cases, genus level in some cases, and species level in a few
cases. We have recently begun more extensive analyses of prey remains in an attempt to
refine our ability to identify remains to the species level. This requires microscopic
analyses of mammal hair, and time-consuming comparisons of minute bone fragments
and teeth with museum reference collections, which in some cases, have yet to be
prepared.
We also palpated all captured and recaptured snakes to determine if we could detect a
food bolus, indicating recent feeding. Because snakes swallow their food whole, it is
often possible to determine if they have fed recently by the presence of a large bulge or
bolus in the stomach or fore gut. However, due to the strength of their axial muscles, and
the action of their digestive enzymes, a snake could have eaten recently, but an obvious
bolus may not be detectable. Via palpation, it is often possible to feel the prey item in the
gastrointestinal tract. However, in most cases, it is difficult to unambiguously define
prey items. Therefore, we only included prey items if we were absolutely certain they
were present.
We kept detailed records of several feeding episodes, which we observed under natural
conditions throughout the course of the study. Although we did not observe feeding
often enough to have any statistical significance, the episodes we observed provide us
with valuable information on the natural history of tiger rattlesnakes.
Habitat Analyses
We examined microhabitat and macrohabitat use. For microhabitat analyses, in 1997 we
recorded data on several variables within a 1-m2 area centered around each snake
location. We waited until radiotelemetered rattlesnakes moved to another location before
collecting microhabitat data to avoid disturbing the snakes. We gathered data at random
sites throughout each snake home range, which allowed us to compare microhabitat use
versus availability using logistic regression analysis, which allowed us to make
inferences about the preferred habitat of tiger rattlesnakes. Within each 1-m2 quadrat, we
recorded the percentage of exposed ground, litter, grass, forb, shrub, tree, cactus, and
total canopy cover. We recorded whether or not a woodrat midden was present, and the
distance to the nearest midden if one was not present. We recorded data on geomorphic
substrate type, which was based on particle size and fell into seven categories: bedrock,
boulder, rock, gravel, pebble, sand, and soil. We recorded the dominant species of grass,
forb, shrub, tree, and cactus. And, we recorded the slope and aspect of each snake
location.
Tiger Rattlesnake Ecology and Management – Goode & Wall 9
To compare macrohabitat use versus availability, we created a georeferenced map of the
TVR study site based on tiger rattlesnake habitat types. Habitat types were based on our
observations of tiger rattlesnake movement patterns. We identified four habitat types:
exposed rock outcrops on ridges, rocky slopes, disected bajada, and xeroriparian wash
consisting of the terrace with soil development, and the sandy active channel. We created
the habitat map by walking the perimeter of each habitat type using a Trimble GPS unit.
We generated line data, which were differentially corrected using carrier phase post-processing,
to obtain 1-3 m accuracy. We analyzed habitat data by overlaying the habitat
map with home range polygons and calculating the proportion of habitat types used
compared to the proportion of habitat types available within each home range. At the
landscape scale, we compared the proportion of tiger rattlesnake habitat types available
within the entire study area with the proportion of habitat types within each home range.
To conduct this analysis, we defined the study area as a polygon containing all known
tiger rattlesnake locations.
Small-Mammal Trapping
We trapped nocturnal rodents in different habitat types and at randomly selected snake
locations at different times throughout the course of the study. Our objective was to
combine the results of small-mammal trapping with diet and fecal analyses to in an
attempt to gain greater insight into foraging ecology and diet of tiger rattlesnakes. In
1997, we set five 16-trap grids centered around snake locations in different habitat types,
which we ran for five nights (400 trap-nights). This pilot effort helped us determine
relative abundance and species diversity at the Tanque Verde Ridge site, and it confirmed
previous observations that small mammals occur in relatively low numbers in rocky
foothill areas of the Sonoran Desert (D. Swann, pers. obs.). In 1998, after studying tiger
rattlesnakes for one year and becoming more familiar with their habitat use, we set four
50-trap grids (with traps spaced at 5-meter intervals) in different habitat types: wash,
bajada, slope and ridge. We ran these grids for 8 nights for a total of 1600 trap-nights.
Where possible, when the number of individuals per species was six or greater, we used
Program CAPTURE to obtain abundance estimates. Unfortunately, capture-recapture
rates were very low in all habitat types, which led to wide confidence intervals, making it
difficult to draw meaningful conclusions.
To determine if small mammals might play a role in tiger rattlesnake movement patterns
at the microhabitat scale, we placed 9-trap grids centered around randomly chosen snake
locations. Each grid was paired with another grid, which was placed at a random
distance and direction from the grid at the snake location. The 9-trap array consisted of
three rows of three traps each with the center trap placed at the snake location (the snake
was no longer present at the location). Traps were spaced at 2-meter intervals. We
compared capture data from the grids at snake locations to the randomly placed grids.
We ran 20 grids (10 at snake locations and 10 at random locations) for four nights each
for a total of 720 trap nights. To examine small mammal species diversity by habitat
type, we pooled all trapping data.
Tiger Rattlesnake Ecology and Management – Goode & Wall 10
Lizard Abundance Index
We used data from our incidental lizard observations (see below) to develop an encounter
rate index of relative abundance and species diversity within different tiger rattlesnake
habitats. As with small-mammal trapping, our goal was to increase our understanding of
tiger rattlesnake foraging ecology and diet by characterizing the available prey base. We
recorded the habitat type (based on tiger rattlesnake habitat use) in which each lizard was
observed, providing us with both the diversity of lizard species and the relative
abundance within each species by habitat type and by season. We then compared this to
tiger rattlesnake habitat use to look for potential patterns.
Incidental Amphibian and Reptile Observations
We recorded all amphibians and reptiles observed while conducting tiger rattlesnake
research, whether radiotracking snakes, walking to and from our vehicles, or conducting
other activities such as small-mammal trapping and habitat measurements. Each time an
animal was observed we recorded the date, time, species, and habitat type. We also
recorded sex and age class if discernable. These data were used to examine relative
abundance of lizards, which was then compared to tiger rattlesnake movement patterns.
These data were also gathered to aid the park in current efforts to conduct a
comprehensive inventory of its herpetofauna.
Data Analyses
We used both graphical and statistical techniques to analyze data. We used ANOVA to
analyze morphological data. We used regression to analyze the relationship of tail length
to gender. We used t-tests to analyze differences in movement patterns and home range
size by sex and by season. We used logistic regression to analyze microhabitat data. All
data met assumptions for each statistical test. We considered tests to be statistically
significant at a£ 0.05.
RESULTS AND DISCUSSION
Search Effort
We recorded time spent conducting field activities (e.g., snake hunts, radiotracking) in
order to calculate the number of snakes captured per unit effort (Table 1). Road cruising
was by far the most efficient method, with an average of 4 person-hours required to
encounter a tiger rattlesnake. During dedicated snake hunts, we captured an average of
one tiger rattlesnake per 18 person-hours, which is more than four times the number of
hours needed to capture a snake while road cruising. Tortoise researchers only captured
an average of one tiger rattlesnake per 50 person-hours.
Tiger Rattlesnake Ecology and Management – Goode & Wall 11
Table 1. Number of tiger rattlesnakes captured per unit effort while conducting different
activities at three study areas (TVR = Tanque Verde Ridge, RK = Rocking K Ranch, LR =
Loop Road, μ = mean.)
Site Method Person-Hours Snakes Captured* Person-
Hours/Snake
TVR Snake Hunt
Radiotracking
212
761
12
31
18
25
RK Snake Hunts
Radiotracking
Tortoise Sampling
71
338
1168
4
39
22
18
9
53
LR Road Cruising 140 40 4
Totals 2690 148 μ = 18
*Includes recaptures
Snakes observed per unit effort may be used as an index of relative abundance, and as
such, may be useful for comparing across taxa. This type of encounter rate index may
have utility in a monitoring context, especially when reasonable estimates of absolute
abundance are difficult to obtain, which is usually the case for snakes. However, using
encounter rates as an index of relative abundance is likely to be confounded by a variety
of factors, including species differences in crypticity, habitat use, and activity patterns to
name a few. In any case, standardizing the number of snakes encountered by unit effort
seems necessary if any conclusions about relative abundance are to be drawn.
In comparison to other rattlesnake species, which we observed incidentally during this
study, tiger rattlesnakes appear to be more abundant. We observed 62 western diamond-backed
rattlesnakes during the study, which is an average of 42 person-hours per snake.
We observed only 5 black-tailed rattlesnakes, which is an average of one every 510
hours. Although these numbers would undoubtedly be greater if we were specifically
searching for these species, we feel that they are reflective of the relative abundance of
these rattlesnake species at our study areas.
Road Cruising
We captured a total of 40 tiger rattlesnakes (37 captures and 3 recaptures) on the LR,
(Figure 3; Table 1). We included 5 additional tiger rattlesnakes in our LR sample; 4 were
captured within 800 m of the road by biologists conducting research on tortoises in the
vicinity, and 1 was captured by us in Freeman Wash approximately 200 m from the road.
Tiger rattlesnakes encountered per unit effort varied from year to year (Table 2).
Tiger Rattlesnake Ecology and Management – Goode & Wall 12
Table 2. Summary of the number of tiger rattlesnakes encountered (including 3 recaptures)
on the Loop Road at Saguaro National Park from 1997-2001. The average number of hours
and miles driven required to encounter a tiger rattlesnake are given.
Year Snakes Encountered Hours/Snake Miles/Snake
1997 10 2.0 18.5
1998 16 1.4 16.9
1999 0 0 0
2000 4 11.6 124.3
2001 10 4.8 55.8
We documented 1478 individuals and 27 species of herpetofauna on the LR (Table 3).
The red-spotted toad (Bufo punctatus) was by far the most commonly observed species.
Table 3. Number of individuals of each amphibian and reptile species observed on the Loop
Road from 1997 – 2001. Total number of hours spent road cruising = 141; Total number of
miles driven = 1582.
Species No. Individuals Individuals/Hour Individuals/Mile
Bufo alvarius 340 2.41 0.215
Bufo cognatus 6 0.04 0.004
Bufo spp. 44 0.31 0.028
Bufo punctatus 601 4.26 0.380
Cnemidophorus tigris 2 0.01 0.001
Cophosaurs texanus 8 0.06 0.005
Coleonyx variegatus 130 0.92 0.082
Crotalus atrox 51 0.36 0.032
Crotalus molossus 5 0.04 0.003
Crotalus tigris 40 0.28 0.020
Heloderma suspectum 13 0.09 0.008
Hypsoglena torquata 17 0.12 0.011
Leptotyphlops humilis 1 0.01 0.001
Masticophis flagellum 3 0.02 0.002
Micruroides euryxanthus 1 0.01 0.001
Phrynosoma solare 16 0.11 0.010
Phylorhincus decurtatus 1 0.01 0.001
Pituophis catenifer 3 0.02 0.002
Rhinocheilus lecontei 11 0.08 0.007
Salvadora hexalepis 2 0.01 0.001
Sceloporus clarki 2 0.01 0.001
Scaphiophus couchi 48 0.34 0.030
Sceloporus magister 122 0.87 0.077
Tantilla hobartsmithi 1 0.01 0.001
Tiger Rattlesnake Ecology and Management – Goode & Wall 13
Table 3 (con’t.)
Species No. Individuals Individuals/Hour Individuals/Mile
Thamnophis cyrtopsis 1 0.01 0.001
Urosaurus ornatus 3 0.02 0.002
Uta stansburiana 1 0.01 0.001
Unidentified 14 0.10 0.004
Total 1487 10.54 0.931
The most commonly observed nocuturnal lizard was the banded gecko (Coleonyx
variagatus) and the most commonly observed diurnal lizard was the desert spiny lizard
(Sceloporus magister). The most commonly observed snake was the western diamond-backed
rattlesnake, followed closely by the tiger rattlesnake.
Figure 3. Aerial photograph showing the number of tiger rattlesnakes (n = 36) encountered
while conducting road cruising surveys on the Loop Road as Saguaro National Park. Tiger
rattlesnakes were captured only along a 3.7-mile segment where the road passes through
rocky foothills of the Rincon Mountains. No tiger rattlesnakes were encountered in lower
elevation creosote flats. Total number of hours spend road cruising = 141; total number of
miles driven = 1582.
Visitor
Center
Boundary
7.4 miles
3.7 miles
Creosote Flats
Rocky Foothills
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 14
Road cruising has been a popular method for sampling herpetofauna for decades (Klauber
1935). Due to the secretive nature of many species, it can be difficult to find animals in
numbers great enough to conduct meaningful analyses. This is one of the primary
reasons why herpetofauna have been poorly studied compared to more visible taxa such
as birds and mammals. Road cruising enables the researcher to cover a far greater area in
far less time, and it is generally repeatable over time. Problems associated with road
cruising include the nonrandom placement of roads, bias associated with the potential to
attract animals to warm pavement at night, and the effects of automobiles on the
abundance and behavior of some species.
Capture-Recapture
Not including recaptures, we captured and marked 169 tiger rattlesnakes from four sites
(Figure 4). We recaptured 21 snakes, excluding radio-equipped snakes, which we
periodically recaptured throughout the study to obtain data on growth. Due to low
recapture rates, we did not attempt to estimate population size or survival at any of our
sites.
Figure 4. Tiger rattlesnakes captured by site. TVR = Tanque Verde Ridge; RK = Rocking
K Ranch; LR = Loop Road; RMFD = Rural Metro Fire Department.
The number of tiger rattlesnakes obtained in this study was much higher than we
expected. Anecdotal information on tiger rattlesnakes led us to believe that they were
both rare (Wright & Wright 1957) and difficult to find (Lowe et al. 1986). Based on this
Tiger Rattlesnakes By Site
39
66
42
22
0
10
20
30
40
50
60
70
TVR RK LR RMFD
Site
No. Snakes
Tiger Rattlesnake Ecology and Management – Goode & Wall 15
study, it appears that tiger rattlesnakes can be locally abundant, especially in rocky
foothill areas. In fact, at our study area, tiger rattlesnakes are one of the most commonly
observed snakes.
The low of number of recaptures is probably not surprising based on prior research with
rattlesnakes. Many snake researchers have commented on the difficulty in estimating
population size and survival in snakes due to their secretive lifestyles. The actual
abundance of snakes is likely much greater than their apparent rarity would suggest.
However, given the large number of hours we spent in a relatively small area, it remains
an enigma as to why we have such a low number of recaptures. In any case, when
recapture rates are low, population and survival estimates based on capture-recapture
probabilities tend to have extremely large confidence intervals, thereby limiting their
value. In cooperation with SNP and Arizona Game and Fish Department personnel, we
are exploring the use of distance sampling for estimating tiger rattlesnake abundance.
Demography
Gender (Figure 5) and age-class structure (Figure 6) at all four sites (including RMFD
Sex by Site
0
10
20
30
40
50
TVR RK LR RMFD
Site
N
Males
Females
Figure 5. Sex ratios of all tiger rattlesnakes captured at all four sites from 1997-2001
snakes) were heavily biased towards adult males. Size class structure for all sites
combined reflects a bias towards larger snakes (Figure 7); however, males and females
did not differ in SVL at TV (t = 1.59, df = 36, p < 0.119).
Tiger Rattlesnake Ecology and Management – Goode & Wall 16
Age Class by Site
0
10
20
30
40
50
TVR RK LR RMFD
Site
N
Adults
Sub-Adults
Neonates
Figure 6. Age-classes of all tiger rattlesnakes captured at all four sites from 1997-2001.
Size Class Distribution
0
5
10
15
20
25
30
35
40
250-300
301-350
351-400
401-450
451-500
501-550
551-600
601-650
651-700
701-750
751-800
SVL (mm)
N
Males
Females
Figure 7. Size class distribution of all tiger rattlesnakes captured at all sites combined from
1997-2001.
Tiger Rattlesnake Ecology and Management – Goode & Wall 17
Many studies have documented a strong bias towards large adult male rattlesnakes
(Duvall et al. 1992). Speculation as to why males are easier to find than females
abounds. Males are larger and therefore more conspicuous, which probably makes them
easier to observe. A predominance of data on sex ratios in snakes points toward
equality,making it unlikely that there are more males present in the population. Males are
bigger risk takers, especially in a polygynous mating system where females are a scarce
resource. This is the case with most temperate pit vipers, as females tend to give birth
every 2-3 years meaning that a segment of the female population will be unreceptive in
any given year. This causes males to move even further in pursuit of females, thus
rendering them more likely to be observed.
We observed interesting interpopulational differences in age-class structure among our
study areas. During the first two years of the study, we did not observe a single subadult
tiger rattlesnake. After processing 70 adult snakes, we finally encountered a subadult at
TVR in late August of 1999. This subadult remains the only one we observed at TVR.
Similarly, we have only observed two subadults from the LR and we are yet to obtain a
subadult from RMFD snakes, although we did acquire one neonate from RMFD
personnel.
In contrast, we have encountered 16 subadults and three neonates from the RK
population. Considering how close it is to the LR and TVR populations (2-8 km), this
was a surprising difference. Marked differences in everything from body size to
physiology have been documented in rattlesnakes (Beaupre 1995). However, the rock
rattlesnake populations that Beaupre (1995) studied were at significantly different
elevations, which may have accounted for the observed differences. Our study sites are
very similar in elevation, varying by no more than 750 m, with significant overlap in
elevations among sites. We are beginning to investigate other potential differences in
these geographically close populations. For example, preliminary data suggest that tiger
rattlesnakes at the TVR site eat predominantly small mammals, but snakes at the Rocking
K site eat a greater proportion of lizards. We have recently begun microsatellite DNA
analyses to explore these differences in more detail.
Morphology
Raw data for all snakes are shown in Appendix A. We summarized processing data for
all snakes and all sites combined (Table 4), and by gender and age class for each site
(Table 5).
Tiger Rattlesnake Ecology and Management – Goode & Wall 18
Table 4. Morphometric data (mean ± standard error) for all tiger rattlesnakes from all sites
combined from 1997-2001. All lengths and widths are in millimeters (mm).
All Sites Combined
Parameter Females Males
N 52 117
Percent adult 81% 89%
Snout-vent length* 573 ± 10 650 ± 10
Tail length* 40 ± 3 61 ± 3
Mass* 192 ± 9 287 ± 11
Head length 25 ± 2 27 ± 2
Head width 19 ± 1 20 ± 2
Number of segments 7 ± 2 7 ± 1
Rattle length 31 ± 3 35 ± 3
Percent with broken rattle 61% 81%
* = significant at a = 0.05
Snout-vent length varied by sex and by site (Figure 8). Males were longer (F = 16.50, df
= 1, p < 0.0002), heavier (F = 11.69, df = 1, p < 0.0013), and more massive per unit body
length than females. Males had 50% longer tails than females, and the ratio of tail length
to SVL was greater in males (t = 19.71, df = 167, p < 0.0001). Simple regression
revealed that there was no overlap in the range of tail to SVL ratio between males (1.387
+ 0.0925 (SVL) = tail, r2 = 0.74, n = 116, mean = 61.5 mm) and females (3.797 + 0.064
(SVL) = tail, r2 = 0.80, n = 53, mean = 40.7 mm) indicating that this is a reliable
character for sexing tiger rattlesnakes (Figure 9). Males tend to have both longer and
wider heads than females, but not relative to their body size.
Most snake species show marked sexual size dimorphism, with males being the larger of
the sexes (Shine 1978). Tiger rattlesnakes appear to conform to this general pattern.
Various hypotheses have been proposed for why males tend to be larger than females.
Among these hypotheses is the assertion that males are larger so they can be more
effective in male-male agonistic encounters (Beaupre & Duvall 1998). However, this
runs counter to the notion that large female body size should be selected for because
Tiger Rattlesnake Ecology and Management – Goode & Wall 19
larger females can give birth to more offspring, which is the case in many snake taxa
(Shine 1978).
Table 5. Body and head size data (mean ± standard error) for all tiger rattlesnake age
classes at all sites combined from 1997-2001. TVR = Tanque Verde Ridge, RK = Rocking K
Ranch, LR = Loop Road, RMFD = Rural Metro Fire Department, F = female, M = male, SA
= subadult, SVL = snout-vent length, TL = tail length, HL = head length, HW = head width.
TVR RK LR RMFD
Parameter F M SA F M SA F M SA F M
N 14 24 1 13 34 16 10 30 2 5 16
SVL 627
± 6
659 ±
8
511 605 ±
7
667 ±
8
479 ±
10
604 ±
7
687 ±
8
511 ±
7
575 ±
8
678 ±
8
TL 44 ±
2
61 ±
3
38 42 ±
2
64 ±
2
41 ±
3
42 ±
2
66 ±
3
42 ±
3
42 ±
2
63 ±
3
Mass 244
± 7
287 ±
9
113 179 ±
5
295 ±
9
91 ±
7
233 ±
8
341 ±
9
139 ±
7
240 ±
9
327 ±
11
Mass/SV
L
0.38
9
0.436 0.221 0.296 0.442 0.190 0.386 0.496 0.272 0.417 0.482
HL 27 ±
1
27 ±
2
25 26 ±
1
28 ±
1
22 ±
2
26 ±
2
28 ±
1
26 ±
1
24 ±
1
28 ±
1
HW 20 ±
1
21 ±
2
17 19 ±
1
21 ±
1
17 ±
1
20 ±
1
21 ±
1
21 ±
1
19 ±
1
21 ±
1
HL/SVL 0.043 0.041 0.048 0.043 0.042 0.045 0.043 0.040 0.050 0.041 0.041
Tail length is often used to distinguish between sexes in snakes. Presumably, males have
longer tails to accomodate their reproductive organs which are located in the tail.
Another character used to sex snakes is number of subcaudal scales, with females having
fewer subcaudals due to their shorter tail length. However, we observed some overlap in
the number of subcaudals, suggesting that tail length relative to SVL may be a more
reliable way to sex some snake species.
Reproduction
We observed reproductive activity (accompaniment, courtship, and copulation) only
during the summer monsoon season (Table 6). We defined the monsoon season as
beginning when the study area received its first substantial rainfall and ending when it
received its last rainfall. In all years, the onset of the monsoon season was obvious due to
a marked change from extremely dry to extremely humid weather conditions. Not
surprisingly, we also determined that adult males produce semen more during this period
(July-September) than during the spring or fall (Figure 10). Both males and females
Tiger Rattlesnake Ecology and Management – Goode & Wall 20
Adult Size by Site
560
580
600
620
640
660
680
700
0 1 2 3 4 5
Site
SVL (mm)
Male
Female
RK TVR LR RMFD
Figure 8. Adult size by sex at all four sites from 1997-2001. RK = Rocking K Ranch;
TVR = Tanque Verde Ridge; LR = Loop Road; RMFD = Rural Metro Fire Department.
Figure 9. Graph showing the ratio of tail length (TL) to snout-vent length (SVL) in male
tiger rattlesnakes (n = 169). Females (squares) exhibited no overlap with males
(triangles) indicating that TL to SVL ratio is a reliable character for determining sex in
tiger rattlesnakes. See text for equations and t-statistics.
0
10
20
30
40
50
60
70
80
400 450 500 550 600 650 700 750 800
SVL (mm)
TL (mm)
Males
Females
Tiger Rattlesnake Ecology and Management – Goode & Wall 21
Table 6. Date ranges by year of tiger rattlesnake reproductive activity (accompaniment,
courtship, and copulation) compared to annual date ranges for the wet summer season.
Year Reproductive Activity Monsoon Season
1997 08/27 – 09/06 07/17 – 09/11
1998 07/08 – 09/22 07/03 – 09/11
1999 07/26 – 09/05 06/26 – 09/04
2000 -- 06/17 – 09/11
2001 07/30 – 08/17 07/03 – 09/14
Total 07/08 – 09/22 06/17 – 09/14
Semen Present By Season
1 2
51
6 8
18
107
27
0
20
40
60
80
100
120
Mar-April May-June July-Sep Oct-Dec
Season
N
Figure 10. Seasonal incidence of semen expressed from the hemipenal shafts of male tiger
rattlesnakes at all four sites from 1997-2001. White bars = semen present, black bars = all
captures and recaptures combined.
paired with multiple partners (range = 2-5 partners) over the course of a single breeding
season. Reproductive associations of male and female snakes lasted an average of 3.8
days (range = 1-9 days). In some cases, a male snake appeared to follow the same female
over the course of a few to several days. In 1997, we were alerted by a resident living at
the park boundary that a pair of tiger rattlesnakes was mating in his yard. We captured
Tiger Rattlesnake Ecology and Management – Goode & Wall 22
and implanted radiotelemeters into both animals. The male proceeded to follow the
female over the course of several days, and we found him courting her on multiple
occasions. Mating interactions between radiotagged individuals occurred on several
occasions during 1998, a year of high reproductive activity, which coincided with a year
in which we were radiotracking several male and female tiger rattlesnakes.
Overall, we observed tiger rattlesnakes engaged in some manner of reproductive activity
3.6% of the time (range = 0%-7.8%) when located. Far more reproductive activity
occurred in 1998 than in any other year (Figure 11). A greater proportion of females
gave birth in 1999 than in other years as well (Figure 12), providing further evidence that
1998 was an important breeding year (litters are born the year after mating takes place).
Reproductive Activity by Year
1
22
4
0
3
4
18
1
0
1
0
10
1
0 0
0
5
10
15
20
25
1997 1998 1999 2000 2001
Year
N
Accompaniments
Courtships
Copulations
Figure 11. Tiger rattlesnake reproductive activity by year at the Tanque Verde Ridge study
site from 1997-1999 and at the Tanque Verde Ridge and Rocking K study sites combined
from 2000-2001.
Based on palpation of 15 gravid females, we determined average tiger rattlesnake litter
size to be 3.4 ± 1.0 (SD) (range = 2-6). The actual number of young born is probably
lower than our estimates, however, since we mostly performed follicle counts and not all
follicles are ovulated. In any case, the exact number is small compared to litter sizes of
other rattlesnake species found in Arizona (Table 7). Based on five females, which we
captured to assess their reproductive condition, parturition occurred from August 1 to
August 20. We were only able to obtain morphological data on one litter consisting of 5
neonates, which were born to a snake captured by RMFD personnel (Table 8). Neonates
from this litter first shed their skin 8-9 days post-parturition.
Tiger Rattlesnake Ecology and Management – Goode & Wall 23
Proportion Giving Birth
0
5
10
15
20
25
1997 1998 1999 2000 2001 2002
Year
N
Figure 12. Number and proportion of tiger rattlesnakes giving birth by year at the Tanque
Verde Ridge and Rocking K study sites from 1997-2001. White bars = gave birth; black
bars = did not give birth.
Table 7. Average litter size of several rattlesnake species in Arizona (from Lowe et al. 1986).
Species Average Litter Size
Crotalus. atrox 9
C. viridis 9
Sistrurus catenatus 9
C. scutulatus 8
C. cerastes 7
C. molossus 7
C. mitchellii 5
C. willardi 5
C. pricei 5
C. lepidus 4
C. tigris 3.4 ± 1.0 (range 2-6)
Tiger Rattlesnake Ecology and Management – Goode & Wall 24
Table 8. Morphological data (mean ± standard error) for the litter born to CRTI #55, a
female collected by the Tucson Rural-Metro Fire Department in 1999.
Littermate Born First
Shed
Sex SVL TL Mass HL HW
1 8/1/99 8/10/99 M 259 25.0 19.5 17.5 13.5
2 8/1/99 8/9/99 M 262 26.0 21.2 19.0 13.5
3 8/1/99 8/9/99 M 265 24.1 21.0 19.0 13.0
4 8/1/99 8/9/99 M 263 24.0 21.5 18.0 13.0
5 8/1/99 8/9/99 F 261 20.8 22.0 20.0 13.0
Mean 4M:1F 262
±
1.5
24.0
±
1.4
21.0
±
0.97
18.7
±
0.99
13.2
±
0.52
On average, adult females give birth once every three years as indicated by the fact that
only 33% of females captured during the course of this study were gravid. However,
there was significant individual and annual variation. For example, more than half of the
adult females we processed in 1999 produced a litter in that year, and two snakes gave
birth in both 1998 and 1999. Gravid snakes are not significantly longer than non-gravid
adult females (t = 0.96, df = 42, p < 0.34), but as expected, they are significantly heavier
(t = 2.30, df = 38, p < 0.03) (Table 9). One gravid female we found measured 521 mm
SVL, the smallest reproductively mature tiger rattlesnake yet recorded (cf. Goldberg
1999).
Table 9. Size (mean SVL ± standard error) of adult female tiger rattlesnakes that became
gravid at any time during the study compared to size of females who were never found to be
gravid, and to all adult females. Data are from all sites combined from 1997-2001
Category SVL Mass N
Gravid Females 602 ± 7 245 ± 8 16
Non-Gravid Females 612 ± 7 211 ± 7 26
All Adult Females 608 ± 7 221 ± 8 42
Tiger rattlesnakes mate during the monsoon season. Females store sperm over the
winter, ovulate upon emergence from their dens in the spring, and gestate until late July
or early August, when they give birth. Spermatogenesis commences in late spring or
early summer, and females initiate vitellogenesis during the summer monsoon of a
reproductive year.
The type of mating system in effect is difficult to determine because of the variation in
both male and female reproductive behavior. Tiger rattlesnakes may exhibit prolonged
Tiger Rattlesnake Ecology and Management – Goode & Wall 25
mate-searching polygyny (PMSP), characterized by females that are irregularly spaced,
difficult to locate, and/or infrequently receptive (Duvall et al. 1992). Under this system,
males find few if any females during the mating season and rarely encounter other males,
resulting in very little male-male agonistic behavior (i.e., combat). We did not observe
combat during the five-year study, and males in most years found only a single female, or
no females at all.
In contrast, female defense polygyny (FDP), in which females are easier to locate, more
abundant, and/or sexually receptive for longer periods of time (Duvall et al. 1992), may
best describe the mating system in tiger rattlesnakes. Under FDP, males are expected to
engage in serial mate guarding, attempting to monopolize the reproduction of multiple
females in succession (Duvall et al. 1992). Males are also more likely to come into
contact with other males, with combat a likely result. Indeed, we observed what
appeared to be mate guarding on multiple occasions, and male-male combat in tiger
rattlesnakes has been observed (P. Holm, pers. comm.). Further, while we witnessed no
combat at our study sites, we did observe a male snake initiate combat behavior as we
attempted to photograph him while copulating with a radiotagged female. The male rose
up to combat our snake tongs while we used them to brush aside vegetation, which was
obscuring our view of the copulating pair.
None of this information is convincing evidence of FDP, however, because long-term
accompaniment does not necessarily represent mate guarding. Courtship and copulation
behavior in male rattlesnakes is cued largely by pheromones that females produce upon
shedding (Schuett 1992). Therefore, it is possible that males that remain with females for
extended periods of time are simply waiting for them to shed. We observed a male
vigorously courting a road-killed female, indicating the importance of chemosensory
information in reproduction. In short, we need more data to determine the precise nature
of the mating system of tiger rattlesnakes.
Tiger rattlesnake reproduction is extremely variable from year to year and appears to be
significantly correlated with rainfall. In 1998, when we observed a dramatic increase in
mating activity, we also received record amounts of rainfall due to a pronounced El Niño
event (Figure 13). Rodents in the desert Southwest are known to breed prolifically
following intense rainy seasons, in particular after abnormally wet winters (Y. Petryszyn,
pers. comm.).
It is possible that female tiger rattlesnakes benefited from an elevated prey base in the
spring and summer of 1998, accumulating sufficient fat reserves to initiate the
energetically costly process of vitellogenesis. Snakes at our study sites averaged one
litter every three years, but reproduction varied greatly from individual to individual.
Two females gave birth in successive years (1998 and 1999), indicating that tiger
rattlesnakes can reproduce annually if females have sufficient energy reserves.
Tiger Rattlesnake Ecology and Management – Goode & Wall 26
Rainfall by Season and Year
0
100
200
300
400
500
600
1997 1998 1999 2000 2001
Year
mm
Wet Summer
Winter
Figure 13. Seasonal rainfall by year at Saguaro National Park. Data are presented in
“water years” meaning that the year begins at the onset of winter rains and ends when the
summer rains end.
Growth
Females and males did not differ in annual growth rate (t = 0.58, df = 38, p = 0.57). Both
sexes averaged a yearly SVL increase of 2.5%. Not surpisingly, virtually all growth
occurred during the snakes’ active season (April-early November) rather than over the
winter, when no feeding took place (Figure 14).
We observed growth-rate differences between sites. Snakes at TVR grew more than
twice as fast as snakes at the RK (Figure 15); however, these differences were not
statistically significant (F = 2.57, df = 33, p = 0.14). Site differences in growth rates may
be a consequence of divergent diets at the two sites. Snakes at TVR consumed primarily
small mammals, relatively large prey with a high energy yield, while tigers at RK ate
mostly lizards (see below). Thus, snakes at TVR may be accruing more energy, and as a
result may be able to devote more resources to growth.
Tiger Rattlesnake Ecology and Management – Goode & Wall 27
SVL Growth by Season
2.21
0.30
0
1
2
3
Winter Active Season
%
Figure 14. Mean annual growth in SVL for all tiger rattlesnakes combined, 1997-2001.
Average SVL Growth/Year
2.8
1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
TVR RK
Site
%
Figure 15. Average growth rate per year of all tiger rattlesnakes combined by site.
Tiger Rattlesnake Ecology and Management – Goode & Wall 28
Our data suggest that implantation of radiotelemeters may retard growth in tiger
rattlesnakes. Snakes without radios grew more than twice as rapidly as snakes with
radios (F = 8.96, df = 37, p = 0.01; Figure 16). Perhaps implanted snakes spend more
time basking to recover from surgery, compromising other activities such as foraging. It
seems reasonable to assume that some energy must be allocated to healing at the expense
of growth. Indeed, snakes with radios shed more often than those without (1.3 sheds/year
and 1.1 sheds/year respectively), although this difference was not statistically significant
(t = 1.39, df = 24, p = 0.18). Shedding in response to injury is a known response in
snakes (Rubio, 1998).
However, short-term effects of surgery are not likely to be a major factor in growth-rate
disparity, because snakes that had been implanted for two years still exhibited diminished
growth. Perhaps the radiotag implant is constantly being “fought off” by the snakes
immune system. Such a prolonged heightened immune response would of course require
energy. It is also possible that the bulk of the transmitter may render the snake less
mobile and as a result, less able to obtain prey. At this point, we cannot definitively say
Average SVL Growth/Year
1.5
3.9
0
1
2
3
4
5
Radio Snakes NR Snakes
%
Figure 16. Average growth rate of tiger rattlesnakes implanted with a radiotag (Radio
Snakes) and snakes without a radiotag implant (NR Snakes). Although snakes without
implants grew more than twice as much as snakes with implants, the results were not
statistically significant (t = 0.61, df = 51, p < 0.512) due to high individual variation in
growth rates.
Tiger Rattlesnake Ecology and Management – Goode & Wall 29
how transmitter implantation impacts tiger rattlesnake growth (or any other aspect of
their biology). More research is needed to determine how the powerful and increasingly
pervasive technique of radiotelemetry is affecting the biology and behavior of study
organisms. Recognizing that effects of radiotelemetry implants may be negative is
important, because it enables us to better determine potential sources of error in our data.
Spatial Ecology
We implanted radiotelemeters into 35 tiger rattlesnakes, which we located 2627 times
(Figure 17). We utilized several movement and space-use parameters to compare the
spatial ecology of males and females (Table 10). Females had smaller home ranges than
males (Table 10; Figure 18), which is not surprising given that in most rattlesnake species
males actively search for relatively sedentary female mates (Duvall et al. 1992). Both
sexes exhibited seasonal differences in home range size and movement patterns, with
conspicuous spikes occurring in wet summer, when most feeding and all mating takes
place (Table 10; e.g., Figure 19). However, some seasonal activity differences between
Figure 17. Digitized aerial photograph showing 2627 locations of 35 tiger rattlesnakes at
the Tanque Verde Ridge study area (left) and the Rocking K Ranch study area from 1997-
1998 and 2000-2001. Data for 1999 are not included because of technical difficulties with
GPS post-processing. 1997 = purple, 1998 = orange, 2000 = blue, and 2001 = yellow.
Boundary
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 30
0 2 km
Figure 18. Minimum convex polygon home ranges for selected females (top) and males
(bottom) at the Tanque Verde Ridge and Rocking K study areas. There is substantial
overlap in male home ranges, therefore only the home range outline is displayed.
N
0 1 km
0 1 km
N
Tiger Rattlesnake Ecology and Management – Goode & Wall 31
the sexes were apparent. Females moved more during the spring than males did (Table
10), which may be explained by the fact that females emerged from hibernation an
average of 18 days (April 5 for females as opposed to April 23 for males) sooner than
males did. By May and June (dry summer), males were more active and mobile than
females and remained so until entering their winter dens in late October or November.
Males, but not females, exhibited annual differences in home range size and movement
patterns in 1998 compared to 1997 (Figure 20). As noted above, 1998 was a very wet
year during which a tremendous amount of tiger rattlesnake reproductive activity
occurred. Thus increased male movement in 1998 probably reflected greater mate-searching
activity stimulated by abnormally high rainfall. As female movement patterns
remained relatively constant, differences in foraging behavior from year to year were not
implicated.
We have not yet intensively investigated space use by site, but some differences do seem
to exist. For instance, tiger rattlesnake movements at the RK were of a much more linear
(north-south) nature than at TVR (Figure 17). We believe this is due to topographical
differences between sites. At RK, one major north-south wash drains most of the study
area, while TVR is characterized by a network of arroyos. As tiger rattlesnakes tend to
use washes during the active season (see below), wash orientation probably has an effect
on snake movement patterns.
Feeding and Diet
Prior to this study, the feeding habits of tiger rattlesnakes were not well known. The
species’ small head size has led to the suggestion that it consumes primarily lizards
(Lowe et al. 1986, Ernst 1992). However, data from fecal samples revealed that tiger
rattlesnakes take a variety of prey types and that they appear to feed predominantly on
small mammals (Figure 21).
Both male and female tiger rattlesnakes foraged most actively and most successfully
during the summer monsoon season (Figure 22). However, some gender differences in
diet did exist, although these differences were not statistically different (C2 = 0.89, df = 1,
87, p = 0.35). Males consumed an approximately equal proportion of lizards and rodents,
while females ate more small mammals (Figure 23). This difference is probably not a
consequence of divergence in head or body size, because males are larger than females.
Rather, the difference may result from greater energy requirements of adult females.
Vitellogenesis and embryo development are extremely costly activities; perhaps females
need larger, higher-energy prey than males do. Another possibility is that diet differences
are a residue of activity and movement differences between the sexes. Males move more
frequently and travel greater distances than females, especially during the wet-summer
active season. Therefore, males are likely to encounter more lizards (either active or
resting; see below) than females. Females may be more restricted to rodents by their
more sedentary habits.
Tiger Rattlesnake Ecology and Management – Goode & Wall 32
Table 10. Summary of movement and home range data (mean ± standard error) for tiger
rattlesnakes at Tanque Verde Ridge and Rocking K from 1997-2001 (N = 2627). Data from
individual snakes were not used in the analyses unless the number of radiotelemeter fixed
was at least n = 30.
*Significant at a = 0.05
Season Parameter Males Females
Total Total Distance Moved* 4009 ± 326.4 1578 ± 176.5
Distance/Movement* 92.7 ± 7.3 42.4 ± 6.4
Distance/Day* 22.4 ± 2.4 9.8 ± 1.2
MCP* 15.0 ± 4.2 3.3 ± 0.5
95% Active Kernel* 19.1 ± 4.8 4.6 ± 0.8
50% Core Area* 3.4 ± 0.8 0.9 ± 0.2
Spring Total Distance Moved 130 ± 53.2 219 ± 67.5
Distance/Movement 24.0 ± 8.3 34.8 ± 13.1
Distance/Day 3.7 ± 1.5 6.3 ± 2.0
MCP 0.2 ± 0.2 0.3 ± 0.2
95% Active Kernel 2.6 ± 1.5 3.1 ± 2.6
50% Core Area 0.6 ± 0.4 0.5 ± 0.4
Dry Summer Total Distance Moved* 481 ± 206.2 103 ± 45.2
Distance/Movement 61.9 ± 24.9 11.9 ± 4.2
Distance/Day* 14.6 ± 7.4 2.2 ± 1.0
MCP* 1.5 ± 1.1 0.05 ± 0.02
95% Active Kernel* 2.9 ± 1.0 0.3 ± 0.1
50% Core Area* 0.6 ± 0.2 0.05 ± 0.02
Wet Summer Total Distance Moved* 2142 ±281.4 707 ± 106.9
Distance/Movement* 91.0 ± 11.2 32.6 ± 4.2
Distance/Day* 34.9 ± 4.4 11.4 ± 1.6
MCP* 10.1 ± 1.8 1.7 ± 0.6
95% Active Kernel* 16.9 3.8 3.8 ± 1.3
50% Core Area* 3.0 ± 0.9 0.8 ± 0.2
Fall Total Distance Moved* 1002 ± 263.9 438 ± 61.5
Distance/Movement* 65.3 ± 13.9 30.9 ± 5.1
Distance/Day* 28.4 ± 7.3 11.7 ± 2.0
MCP* 5.0 ± 1.8 0.7 ± 0.1
95% Active Kernel* 15.2 ± 5.9 2.7 ± 0.6
50% Core Area* 3.1 ± 1.1 0.6 ± 0.2
Tiger Rattlesnake Ecology and Management – Goode & Wall 33
Figure 19. Minimum convex polygon home ranges for wet summer compared to the rest of
the year for a male tiger rattlesnake at Tanque Verde Ridge in 1998. This pattern of
seasonal home range use was typical for all tiger rattlesnakes, although more so for males
than for females.
We also observed feeding differences between sites (C2 = 4.73, df = 1, 74, p = 0.03).
Tiger rattlesnakes took more lizards than rodents at RK, but nearly three times more
rodents than lizards at TVR (Figure 24). We did not observe snakes to employ divergent
foraging strategies from site to site. Rather, our data reveal that lizards are simply more
abundant at RK (Table 11).
Of 29 identified lizard remains in tiger rattlesnake feces, 27 were whiptails
(Cnemidophorus species). Whiptails are active, fast-moving diurnal lizards that are
extremely common at RK and less so at TVR (Table 11). The few feeding episodes we
observed, suggest that tiger rattlesnakes ambush whiptails that wander into striking range
(as they do with rodents); however, active searching for sleeping or resting lizards may
also be important. We witnessed what appeared to be active foraging on multiple
occasions, as snakes were observed to move throughout woodrat middens and other
rodent burrow systems, exhibiting increased tongue-flicking.
Wet Summer
Rest of the Year
Tiger Rattlesnake Ecology and Management – Goode & Wall 34
Figure 20. Minimum convex polygon home ranges for selected males (top) and females
(bottom) at the Tanque Verde Ridge study area in 1997-1998. Male home range size varied
in size from year to year, but female home range size did not.
1997
1998
1998
1997
N
0 1 km
1997
1997
1998
1998
N
0 1 km
Tiger Rattlesnake Ecology and Management – Goode & Wall 35
Figure 21. Percent of prey types in tiger rattlesnake diet for 105 tiger rattlesnakes from all
sites combined from 1997-1999.
Percent Bolus by Season
0%
5%
10%
15%
20%
25%
March-April May-June July-September October-November
Season
Figure 22. Percentage of tiger rattlesnakes (all sites and all years combined) found to
contain a food bolus in their gastrointestinal tract at different times of the year. Food boli
were detected via external palpation.
Tiger Rattlesnake Diet
0
10
20
30
40
50
60
Mammal Reptile Avian No prey
Prey Type
%
Tiger Rattlesnake Ecology and Management – Goode & Wall 36
Diet By Sex
0
10
20
30
40
50
60
70
Females (N=33) Males (N=52)
Relative Proportion (%)
Rodents
Lizards
Figure 23. Proportion of male and females tiger rattlesnakes eating rodent and lizard prey
at all site and in all years combined.
Table 11. Relative abundance, by site, of lizard species (all except Heloderma suspectum)
considered potential prey of tiger rattlesnakes.
Lizard Category TVR RK Total
Prey lizards 364 527 891
Cnemidophorus individuals 149 227 376
Prey lizards/hour search effort 0.48 1.56 0.81
Cnemidophorus individuals/hour search effort 0.19 0.68 0.34
Tiger Rattlesnake Ecology and Management – Goode & Wall 37
Diet By Site
37
14
16
21
0
5
10
15
20
25
30
35
40
45
TVR RK
N
Rodents
Lizards
Figure 24. Number of tiger rattlesnake fecal samples containing rodent and lizard remains
by site.
Habitat
Logistic regression analysis performed on microhabitat data from 1997 revealed
differences in habitat use between sexes that varied by habitat type (uplands [= slope and
ridge] versus lowlands [= wash and bajada]) (Table 12). The differences were based on
comparison with random locations within tiger rattlesnake home ranges. In lowlands,
female tiger rattlesnakes were associated with significantly greater shrub, tree and canopy
cover than males. Males were found more often in prickly pear cactus than females and
males were also found closer to woodrat middens. In uplands, females were associated
with greater grass and tree cover than males.
These results seem to reflect the tendancy for females to remain in cover more often than
males, which is likely a byproduct of males’ tendancy to move more often than females.
Increased movement on the part of males is in turn related to the fact they must actively
search for more sedentary females in order to obtain mating opportunities. Likewise, the
tendancy for males to be found in association with woodrat middens reflects their
predilection to actively forage, whereas females ambush more often (see Diet and
Feeding).
Tiger Rattlesnake Ecology and Management – Goode & Wall 38
Table 12. Logistic regression analysis of microhabitat data for locations (N = 203) of 10
tiger rattlesnakes, Tanque Verde Ridge site, 1997. Lowlands = wash and bajada, uplands =
slope and ridge. P>F = ANOVA, P>C2 =Kruskal-Wallis ANOVA on ranks, which was used
to determine final probabilities because the variables were not normally distributed.
*P < 0.10
**P < 0.05
Tiger rattlesnakes exhibited pronounced seasonal differences in habitat use (Figure 25).
The typical pattern consisted of very low activity in spring and dry summer as snakes
remained mostly on rocky slopes with some individuals moving into washes. We
observed a dramatic increase in movment during wet summer as snakes primarily used
wash and bajada areas to forage and mate. In fall, tigers continued to move, although less
so than in wet summer, as snakes made their way back to their winter dens located on
rocky slopes above washes and bajada areas.
Lowlands
Category Male Female P>F P>C2 Sex
Midden Distance 3.68 6.13 0.057 0.058* F
% Exposed 31.18 30.78 0.964 0.962
% Litter 18.82 5.81 0.039 0.754
% Grass 14.41 18.75 0.581 0.501
% Forb 1.47 4.09 0.514 0.416
% Shrub 3.23 24.77 0.021 0.063* F
% Tree 0.59 7.73 0.040 0.009** F
% Cactus 30.29 12.16 0.009 0.004** M
% Canopy 10.00 23.00 0.081 0.086* F
Uplands
Midden Distance 6.26 5.33 0.589 0.693
% Exposed 62.12 52.14 0.229 0.294
% Litter 4.24 9.05 0.377 0.360
% Grass 0.76 7.38 0.051 0.088* F
% Forb 6.36 2.62 0.292 0.189
% Shrub 10.30 12.86 0.682 0.984
% Tree 0.76 4.52 0.024 0.051* F
% Cactus 15.45 11.43 0.497 0.231
% Canopy 10.15 9.76 0.954 0.800
Tiger Rattlesnake Ecology and Management – Goode & Wall 39
Figure 25. Tiger rattlesnakes exhibit pronounced seasonal variation in movement patterns
and habitat selection. The habitat map (top) shows a subset of tiger rattlesnake locations
from 1997-1998. The histogram (bottom) shows the proportion of tiger rattlesnake
locations relative to availability of each habitat type.
0
10
20
30
40
50
60
70
Wash Bajada Slope Ridge
%
Available
Spring
Dry Summer
Wet Summer
Fall
Bajada
Plateau
Slope
Ridge
Wash
N
0 250 m
Tiger Rattlesnake Ecology and Management – Goode & Wall 40
Small-Mammal Trapping
Small mammal diversity varied by habitat type at our study sites (Table 13). Although
relative abundance of small mammals varied by habitat type, we were unable to precisely
quantify the differences using mark-recapture data because sample sizes were low. We
had hoped to draw conclusions regarding potential interactions of tiger rattlesnakes and
their small-mammal prey, but dismal trapping success made it difficult. However, we did
document distinct changes in species composition among habitat types. For example,
Chaetodipus intermedius is only found on rocky slopes and ridges, while C. penicilatus is
only found in wash and bajada areas.
These habitat differences may play a role in tiger rattlesnake foraging ecology. We may
be able to address this more thoroughly as we progress with our fecal analyses.
Presumably, we will be able to pinpoint more accurately the rodent species consumed by
tiger rattlesnakes. This will allow us to say more about the effect of habiat type on tiger
rattlesnake diet, which we can then couple with information on season, sex, reproductive
status and body size.
Table 13. Small mammals trapped at the Tanque Verde Ridge site from 1998-1999. CHBA
= Chaetodipus baileyi, CHPE = Chaetodipus peniculatus, CHIN = Chaetodipus intermedius,
PEAM = Perognathus amplus, PEER = Peromyscus eremicus, NEAL = Neotoma albigula.
Habitat
Type Species
Number
Caught
Number
Recaptured
Population
Estimate 95% CI
Wash
Slope
Ridge
Bajada
CHBA
CHPE
CHIN
PEAM
PEER
CHBA
CHPE
CHIN
NEAL
PEER
CHBA
CHIN
PEER
NEAL
CHBA
CHPE
NEAL
50
22
1
7
2
5
3
9
12
6
2
18
4
2
7
17
3
11
15
0
4
0
19
1
1
1
2
2
5
4
1
2
13
0
15
7
23
31
21
14-25
7-17
10-105
23-55
19-33
Tiger Rattlesnake Ecology and Management – Goode & Wall 41
Lizard Abundance Index
We incidentally encountered a total of 46 reptile and amphibian species at TVR and RK
(Table 14), 16 of which were lizards. Lizard species composition differed little between
Table 14. Numbers of individuals and hours required to encounter an individual of all
reptile and amphibian species encountered incidentally at both the TVR and RK sites from
1997-2001.
Species Number of Individuals Hours/Individual
Arizona elegans 1 2550
Bufo alvarius 17 150
Bufo cogntus 2 1275
Bufo punctatus 13 196
Callisaurus draconoides 59 43
Chilomeniscus cinctus 1 2550
Cnemidophorus burti 1 2550
Cnemidophorus flagellicaudus 5 510
Cnemidophorus spp. 279 9
Cnemidophorus tigris 90 28
Cophosaurus texanus 80 32
Coleonyx variegatus 6 425
Crotalus atrox 62 41
Crotalus molossus 5 510
Crotalus scutulatus 1 2550
Crotaphytus collaris 9 283
Eumeces fasciatus 1 2550
Gopherus agassizi 60 43
Heloderma suspectum 37 69
Hyla arenicolor 1 2550
Hypsiglena torquata 3 850
Kinosternon sonoriense 1 2550
Lampropeltis getula 6 425
Leptotyphlops humilis 1 2550
Masticophis bilineatus 13 196
Masticophis flagellum 9 283
Micruroides euryxanthus 3 850
Phrynosoma solare 14 182
Pituophis catenifer 2 364
Rana catesbeiana 1 2550
Rana yavapaiensis 1 2550
Rhinocheilus lecontei 17 150
Salvadora hexalepis 8 319
Sceloporus clarki 80 32
Tiger Rattlesnake Ecology and Management – Goode & Wall 42
Table 14 (con’t.)
Species Number of Individuals Hours/Individual
Scaphiopus couchi 9 283
Sceloporus magister 20 128
Sceloporus spp. 4 638
Thamnophis cyrtopsis 11 232
Urosaurus ornatus 167 15
Uta stansburiana 81 31
sites; we found 15 species at TVR and 13 at RK, and only three (Cnemidophorus burti,
Crotaphytyus collaris, and Eumeces obsoletus) were observed at one site but not the
other. However, obvious differences in lizard relative abundance between sites were
apparent. Lizards were much more common at RK than at TVR. Furthermore, known or
potential prey species (which we defined as all species except Heloderma suspectum
based on body size) were more abundant at RK (Table 11). This pattern held for
whiptails (Table 11), an important prey item of tiger rattlesnakes (see above).
Like tiger rattlesnakes, lizards (including whiptails), were most active and most
commonly observed during the monsoon season (Table 15). Although potentially biased,
because we
Table 15. Relative abundance and encounter rate of tiger rattlesnake prey lizards by season
(season determined by month) at the TVR and RK sites. DS = dry summer; WS = wet
summer.
Season TVR RK Total
Radiotracking
Hours
Prey Lizards/
Tracking Hour
Spring (Mar-Apr) 40 0 40 83 0.48
DS (May-June) 63 89 152 189 0.80
WS (July-Sept) 254 390 644 562 1.15
Fall (Oct-Nov) 3 44 47 206 0.23
Winter (Dec-Feb) 4 5 9 59 0.15
often used washes to travel from site to site, lizards also seemed to favor washes (Table
16), a preference shared by tiger rattlesnakes during their active season. Tiger rattlesnake
activity periods and habitat preferences may therefore have evolved at least in part to take
advantage of lizard prey.
Tiger Rattlesnake Ecology and Management – Goode & Wall 43
Table 16. Relative abundance of tiger rattlesnake prey lizards by habitat type at the TVR
and RK sites from 1997-2001.
Habitat Type TVR RK Total
Bajada 18 52 70
Ridge 11 42 53
Slope 21 113 134
Wash 116 174 290
MANAGEMENT IMPLICATIONS
In addition to studying tiger rattlesnake natural history and ecology, our objective was to
use this knowledge to develop more effective management strategies for rattlesnakes in
general. The results of this research have implications for rattlesnakes that live along the
boundaries of parks and preserves and that move into adjacent urbanized areas. In
addition, our results lead to possible management strategies for how to mitigate the
effects of translocating rattlesnakes away from urbanized areas. And finally, our findings
enable us to predict how the impending Rocking K development may affect rattlesnakes
living in the area.
The TV site is situated along the boundary of SNP adjacent to a low-density residential
housing area. Several radiotelemetered tiger rattlesnakes moved in and out of the park
during the course of the study, and several more non-radiotelemetered snakes were either
captured on private land or found by residents on their property (Figure 26). The
community living along the park boundary at this site has been there for decades, and the
residents living there are very enlightened when it comes to living with wildlife. Several
residents expressed a keen interest in our research and even professed to be rattlesnake
enthusiasts. However, some residents still insisted on killing rattlesnakes found in their
yard. In general, however, the combination of environmentally sensitive landowners and
a low density of residents may bode well for rattlesnakes. Our radiotagged snakes were
found repeatedly in and around peoples’ yards without incident. Most houses in the area
are on lots of 5-40 acres, which seems to give the rattlesnakes plenty of space to move in
without contacting people on a frequent basis. Furthermore, there is only one main road
that provides access to the housing area and it is neither paved, nor does it pass through
tiger rattlesnake habitat. The lack of roads in the area further allows for peaceful
coexistence of rattlesnakes and humans.
When low-density housing areas abut large natural areas, it would appear that
rattlesnakes have a reasonable chance of persisting indefinitely. Of course, this is not
always the situation. In many areas surrounding Tucson and Phoenix, much higher
density urban areas abut parks, preserves, and national forest lands. Many of the
Tiger Rattlesnake Ecology and Management – Goode & Wall 44
residents living in these areas are new to the desert and are unfamiliar with rattlesnakes
and other wildlife. This can lead to a situation in which rattlesnakes may be killed or
humans may be bitten.
Figure 26. Digitized aerial photograph showing the movements of 6 radiotelemetered tiger
rattlesnakes that moved beyond the boundaries of Saguaro National Park during the course
of the study. A total of 12 tiger rattlesnakes were found outside the park boundary,
including 4 snakes that were found by residents living along the edge of the park.
In the near future, SNP will experience unprecedented development along its southern
boundary due to the Rocking K development (Rocking K Specific Plan 1991, 1996). It
seems reasonable to apply what we have learned during the course of this study to predict
the effects of the development on rattlesnakes living in the area. Our pre-development
data seem to point to some obvious predictions. For example, the extensive bajada area
at the north end of the main xeroriparian wash at the RK site will eventually be home to a
large, high-end resort. This area is relatively flat and less rocky, making it much easier
and less costly to develop. Mass grading to make room for a huge building will certainly
leave this area uninhabitable by snakes. Based on movement and home range data, this
bajada area has been used intensively by tiger rattlesnakes. Snakes use this area as they
move from winter den sites on south-facing slopes within the park to the xeroriparian
wash south of the park boundary (Figure 27). The wash is an important area where
snakes congregate in the summer to forage and mate. The resort will effectively cut off
this corridor between the snakes’ winter and summer habitats. We expect the incidence
Boundary
N
0 250 m
Houses
Tiger Rattlesnake Ecology and Management – Goode & Wall 45
of tiger rattlesnake observations in and around the resort to be very high because of its
location between these two critical habitat areas.
Figure 27. Digitized aerial photograph showing movements
of 16 tiger rattlesnakes in relation to the park boundary and
the future site of the Rocking K development resort. Snakes
overwinter on steep slopes and travel through the future
resort site on their way to and from wash and bajada areas.
The movement of rattlesnakes into the developed area sets the stage for what we expect
to be a critical management concern in the future. The primary issue is what to do when
people living, working, and recreating in the area encounter rattlesnakes. One approach
Future
Resort
Site Wash
Slope
Bajada
Tiger Rattlesnake Ecology and Management – Goode & Wall 46
has been to destroy so-called “nuisance” rattlesnakes that come in contact with people.
Killing rattlesnakes is undoubtedly not good for the snakes themselves, and may pose a
threat to the person attempting to kill the snake. Many rattlesnakes, which were
presumed dead, have managed to bite their assailant. Therefore, killing rattlesnakes is
not likely to be an effective option.
Another tactic for dealing with nuisance rattlesnakes, which is the current preferred
method, is to translocate the snakes away from populated areas (Nowak and van Riper
1999). The Rural Metro Fire Department (RMFD) removes an estimated 3,000-5,000
rattlesnakes from the yards of residents living in and around Tucson every year (G. Good,
RMFD, personal communication). The translocation of rattlesnakes has become an
important management concern for a variety of reasons. Rattlesnakes are venomous and
they may pose a serious threat to people living in areas where rattlesnakes are abundant
(although the threat of snakebite is almost always exaggerated). The real victims of
translocation are the snakes themselves. Translocated rattlesnakes show aberrant
movement patterns, and some individuals may even succumb to being translocated
(Reinert and Rupert 1999). Our data indicate that tiger rattlesnakes show remarkable
fidelity to their home ranges, using the exact same rock outcrops, wood rat middens and
even individual shrubs throughout the course of the year and in successive years.
Aberrant movement patterns may be the result of translocating a snake out of its home
range, causing the snake to become disoriented. This can result in even greater
movement by snakes, thereby increasing the chance that they will find their way into
someone’s backyard. Potential effects on snakes residing in areas where translocated
snakes are released are unknown. However, it seems likely that the addition of new
individuals into the area will be detrimental if resources cannot support an increase in the
number of snakes present.
Many tiger rattlesnakes spent the winter on lower elevation slopes and rock outcrops
situated in and around the area slated for development. If these rocky habitats are
removed to make way for the resort and houses, then this is expected to have a negative
impact on any snakes that currently use these areas as winter refugia. Because these
rocky areas are so critical to the life history of tiger rattlesnakes, damage to these areas
should be of heightened concern to wildlife managers and land planners.
Another specific example of how the development may be expected to impact tiger
rattlesnakes is based on the location of the golf course, with fairways placed along the
wash corridor. Tiger rattlesnakes use the wash corridor for foraging and breeding
purposes during the summer active season. This habitat will be virtually eliminated when
replaced by wide-open fairways that provide little or no cover for snakes (or wildlife in
general). This ties into yet another management concern related to the potential effects of
the development on tiger rattlesnake prey. If the diversity, abundance and distribution of
lizards and rodents are altered by the development, then tiger rattlesnake movements and
habitat use can also be expected to change. For example, the primary prey source of tiger
rattlesnakes at RK is whiptail lizards (M.J. Goode, unpublished data), which prefer open
Tiger Rattlesnake Ecology and Management – Goode & Wall 47
desert areas with intermittent shrub cover. Fairways and parking lots are not expected to
support large populations of whiptail lizards, which may result in a reduction of tiger
rattlesnake prey availability. On the other hand, increased water and vegetation
associated with the development may attract rodents, which may in turn attract
rattlesnakes, thereby exacerbating the nuisance rattlesnake problem. In either case, the
effects of the development on rattlesnake prey resources will likely be long term and
subtle, making the effects more difficult to detect.
Predicting the effects of the development on tiger rattlesnakes is speculative, but may
provide an important guide when developing areas in which they live. As for
determining the actual effects of the development on rattlesnakes, we now have critical
baseline data at RK and at the TVR control site within SNP. This will enable us to more
precisely quantify the effects when the development occurs. Only through this rigorous
scientific approach will we be able to make an unbiased assessment of the effects of
urban development on tiger rattlesnakes. These findings can then be applied to other
areas planned for development that abut natural areas such as SNP.
A MANAGEMENT PLAN FOR URBAN RATTLESNAKES
We have identified several threats facing rattlesnakes living in urban and urbanizing
areas. In this section, we list these threats, followed by specific goals and strategies for
removing or mitigating the threats. We also provide information on actions that have
been taken to achieve these goals.
THREAT DIRECT KILLING OF “NUISANCE” RATTLESNAKES
GOAL Educate public about differences between real and perceived threats of
living in proximity to rattlesnakes.
Encourage fire department personnel to inform the public about the risks
(e.g., being bitten) involved in attempting to kill rattlesnakes.
Work with Arizona Poison Control Center at the University of Arizona to
educate the public about the risks of living in proximity to rattlesnakes and
about the proper procedures for how to deal with snakebite.
Inform public of Arizona Game and Fish regulations requiring a hunting
license to kill rattlesnakes.
STRATEGY Develop an educational brochure to distribute to residents living in areas
where rattlesnakes are common.
Tiger Rattlesnake Ecology and Management – Goode & Wall 48
Develop an educational video depicting rattlesnake defensive behaviors
and how they vary by species and ecological context (e.g., distance to
cover, temperature).
Develop interpretive signage at golf courses that include information
about the natural history and ecology of rattlesnakes.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property.
We are currently developing a video depicting typical defensive behavior
of three rattlesnake species that can be used to educate people about what
to expect when they encounter a rattlesnake. It is our belief that wanton
killing of rattlesnakes is mostly due to ignorance perpetuated by myths
and misunderstandings associated with the true nature of rattlesnake
behavior.
Our association with Jude McNally of the Arizona Poison Control Center
goes back nearly 10 years. We have been featured together on several
media events and have worked together to inform the public about
rattlesnakes and the issue of snakebite in general.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Dennis Caldwell, a graphic designed specializing in
herpetofauna, has created and presented examples of signs to the
development supervisor who is in the process of deciding to proceed with
the project.
THREAT TRANSLOCATION OF “NUISANCE” RATTLESNAKES
GOAL Translocate rattlesnakes within their home ranges whenever possible.
Inform and educate public about the spatial ecology of rattlesnakes,
including characteristics of home ranges, typical movement and activity
patterns, and especially, the extreme fidelity that rattlesnakes show to their
home ranges.
Encourage fire department personnel to inform the public about
rattlesnake home range fidelity and to adopt a policy of translocation
within home ranges whenever possible.
Tiger Rattlesnake Ecology and Management – Goode & Wall 49
Work with Arizona Poison Control Center at the University of Arizona to
educate the public about rattlesnake spatial ecology, and to advocate
translocation within home ranges.
STRATEGY Develop an educational brochure that provides information on rattlesnake
spatial ecology to distribute to residents living in areas where rattlesnakes
are common.
Work with fire departments besides RMFD to educate them about
rattlesnake spatial ecology and behavior, and conduct trainings for firemen
to properly translocate rattlesnakes.
Develop an educational program in conjunction with the Arizona Poison
Control Center that focuses on rattlesnake translocation procedures.
Data gathered during the course of this study indicate that tiger
rattlesnakes show very little annual difference in home range location and
use. These data can be used to bolster recommendations to translocate
snakes within their home ranges.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property. This
brochure also contains information about translocation of rattlesnakes.
We are currently developing a video depicting typical defensive behavior
of three rattlesnake species that can be used to educate people about what
to expect when they encounter a rattlesnake. We could easily include
information about rattlesnake spatial ecology and translocation in this
video.
Our association with Jude McNally of the Arizona Poison Control Center
goes back nearly 10 years. We have been featured together on several
media events and have worked together to inform the public about
rattlesnakes and the issue of snakebite in general. Collaborating on an
educational program dealing with issues of rattlesnake translocation would
be a natural next step.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Again, information about rattlesnake spatial ecology and
translocation procedures could be easily incorporated into the text of
sign(s). We could also expand this effort to other golf courses, trailheads,
Tiger Rattlesnake Ecology and Management – Goode & Wall 50
parks and other outdoor venues where rattlesnakes are an issue and where
the potential to reach the public is great.
THREAT RESIDENTIAL DEVELOPMENT
GOAL Design residential developments in a way that will minimize impacts to
rattlesnakes and other herpetofauna.
STRATEGY Work directly with developers during the planning process to design
residential developments that take into consideration relevant aspects of
rattlesnake behavior and ecology.
Work with agencies that regulate residential developments to initiate
regulations that are based on relevant aspects of rattlesnake behavior and
ecology.
Provide movement corridors between winter areas (i.e., rock outcrops) and
foraging areas (e.g., washes and bajada areas).
Establish buffers around rock outcrops and washes, and minimize
destruction of rock outcrops during development.
Maintain low-density zoning in residential areas that abut parks, preserves
and other natural areas.
Encourage the Arizona Game and Fish Department to provide guidelines
to agencies that regulate residential developments.
Encourage developers to support research on the land they are developing
that will give them information on what the effects of the development
might be on rattlesnakes.
ACTION We have worked with the Rocking K Development Company to allow us
to gather baseline data on their land that can be compared to post
development data on rattlesnake ecology and behavior.
We are currently working with Rancho Vistoso Partners, LLC at their
Stone Canyon site in the Tortolita Mountains to study the effects of this
development on rattlesnakes and other herpetofauna This study was
funded by the Arizona Game and Fish Department.
We have received the official endorsement of the Pima County Planning
Department on this study, and on the study in the Tortolita Mountains.
Tiger Rattlesnake Ecology and Management – Goode & Wall 51
THREAT GOLF COURSE/RESORT DEVELOPMENT
GOAL Design golf course and resort developments in a way that will minimize
impacts to rattlesnakes and other herpetofauna.
Educate golfers and guests about differences between real and perceived
threats of living in proximity to rattlesnakes.
STRATEGY Work directly with golf course and resort developers during the planning
process to design golf courses and resorts that take into consideration
relevant aspects of rattlesnake behavior and ecology.
Work with agencies that regulate golf course and resort developments to
initiate regulations that are based on relevant aspects of rattlesnake
behavior and ecology.
Provide movement corridors between winter areas (i.e., rock outcrops) and
foraging areas (e.g., washes and bajada areas).
Establish buffers around rock outcrops and washes, and minimize
destruction of rock outcrops during development.
Maintain low-density zoning in residential areas that abut parks, preserves
and other natural areas.
Encourage the use of “desert-style” golf course designs that minimize the
impact on natural areas and systems.
Maintain as much open space as possible in resort development areas to
facilitate the movement of rattlesnakes.
Use native plants in landscaping along golf courses and in development
areas to maintain natural vegetation communities.
Minimize the use of water developments as they attract non-native species
such as bullfrogs and predatory fish.
Ensure that water developments are designed to enable rattlesnakes and
other wildlife to easily escape if they become entrapped.
Encourage the Arizona Game and Fish Department to provide guidelines
to agencies that regulate golf course and resort developments.
Tiger Rattlesnake Ecology and Management – Goode & Wall 52
Encourage developers and golf course designers to support research on the
land they are developing that will give them information on what the
effects of the development might be on rattlesnakes.
Develop an educational brochure to distribute to golfers and recreationists
using golf courses and resorts where rattlesnakes are common.
Develop interpretive signage at golf courses and resorts that include
information about the natural history and ecology of rattlesnakes.
ACTION We have worked with the Rocking K Development Company to allow us
to gather baseline data on their land that can be compared to post
development data on rattlesnake ecology and behavior.
We are currently working with Rancho Vistoso Partners, LLC at their
Stone Canyon site in the Tortolita Mountains to study the effects of this
development on rattlesnakes and other herpetofauna. In particular, we are
studying the effects of the golf course by riding golf cart paths at night and
by implanting rattlesnakes with radiotelemeters that are using the golf
course.
We have received the official endorsement of the Pima County Planning
Department and the City of Tucson Department of Recreation on the study
in the Tortolita Mountains.
We have approached Stone Canyon Golf Club in the foothills of the
Tortolita Mountains with the idea of placing interpretive signage along the
golf course. Dennis Caldwell, a graphic designed specializing in
herpetofauna, has created and presented examples of signs to the
development supervisor who is in the process of deciding to proceed with
the project.
THREAT ROAD MORTALITY
GOAL Minimize death of rattlesnakes on roads.
STRATEGY Attempt to reduce the number of road that pass through areas where
rattlesnakes are concentrated or through which rattlesnakes must pass,
such as between rock outcrops and washes.
Use signs that inform motorists to use caution in areas where snakes are
known to be abundant.
Tiger Rattlesnake Ecology and Management – Goode & Wall 53
Conduct studies on the effects of roads on rattlesnakes and other
herpetofauna.
ACTION Biologists at Saguaro National Park have been quantifying road mortality
for the past several years and the death toll is extremely high, with an
estimated 40,000 vertebrates per year dying on roads within the Park.
We have suggested that developers at the Stone Canyon site in the
foothills of the Tortolita Mountains place road signs informing residents to
drive with caution to avoid killing snakes and other animals. We are
optimistic that the developers will take our advice when the site becomes
occupied with residents.
THREAT RATTLESNAKE-PET ENCOUNTERS
GOAL Minimize the number of rattlesnake-pet encounters; pets can kill
rattlesnakes and rattlesnakes can either kill pets or result in costly
veterinarian bills.
STRATEGY Develop an educational brochure to distribute to residents living in areas
where rattlesnakes are common that provides guidance on how to make
your house rattlesnake proof.
Encourage residents to keep their pets confined to their yards to minimize
rattlesnake-pet encounters.
Encourage veterinarians to inform their customers about the risks of
rattlesnake-pet encounters.
ACTION The Tucson Herpetological Society has already developed a brochure
entitled Living with Rattlesnakes that attempts to educate the public about
how to deal with rattlesnakes encountered on their property. This
brochure contains information about how to avoid rattlesnake-pet
encounters.
ACKNOWLEDGEMENTS
This study would not have been possible without the contributions of numerous people
and organizations: Scott Breeden, Jennifer Treiber, Chris Scott, Cristina Jones, Roger
Repp, Dennis Caldwell, Dale Turner, Ian Cornelius, Taylor Edwards, Melanie Bucci,
Clint Boal, Chris Davis, Brent Sigafus, Ed Kuklinski, Brian Nelson, Ryan Gann, Chris
Tiger Rattlesnake Ecology and Management – Goode & Wall 54
Fatzinger, James Borgmeyer, Dan Bell, Julia Fonseca, Jeff Moorbeck, Jennifer
Moorbeck, Brent Bibles, Dana Kilbourne, Aaron Kellar, Wendy Kramer, Melissa Gray,
Alejandro Diaz, Craig Billington, Jeff Smith, Bill Savary, Jillian Cowles, Scott Jackson,
George Ferguson, Caren Goldberg, Matt Kaplan, Young Cage, Jill Rubio, Bob Jones,
Melanie Florez, Becky Florez, Kimya Mahzad, Linda Burback, Jill Becker, Frans
Kranenburg, Mechelle Meixner, Randy Babb, Jesus Garcia, Allison Titcomb, Daniella
Patterson, Al Patterson, P.J. Bailey, Carol Crowell, Nancy Fahringer, Keve Sankman,
Irma Sankman, Jesse White, Jeff Karthizer, Kim Kronenberg, Ron Lancaster, Sandy
Lebron, Vivian MacKinnon, Pinau Merlin, Pam Anning, Kristen Beaupre, Don de
Young, Jim Jarchow, Stephanie Cameron, John Warnock, Don Swann, Dave Hardy,
Dave Duvall, Peter Cunio, Dave Prival, Phil Rosen, Andy Holycross, Bill Mannan, Bill
Shaw, Karen Galindo, Craig Wistler, Andy Honaman, Chuck Whitney, Roy Averill-
Murray, Natasha Kline, Larry Norris, Jude McNally, Bob Brandner, Susan Basford, Bob
Lineback, Rich Hayes, Lisa Carder, Dave Anning, Bill Dabney, Aracelli Gonzalez, John
Williams, Jay Laughlin, Meg Weesner, Joel Peterson, Shawnee Riplog, and Cecil
Schwalbe. Special thanks go to Andrea Tuijl, and Remi Tuijl-Goode for their patience
and support. Funding sources included: Arizona Game and Fish Department Heritage
Fund, Southwestern Parks and Monuments Association, Tucson Zoological Society, Reid
Park Zoo Teen Volunteers, Denver Zoological Society, National Park Service, Oklahoma
State University, Desert Southwest Cooperative Ecosystem Studies Unit, University of
Arizona, and Saguaro National Park.
LITERATURE CITED
Amaral, A. do. 1929. Notes on Crotalus tigris Kennicott 1859. Bulletin Antivenin
Institute of America. 2:82-85.
Armstrong, B.L., and J.B. Murphy. 1979. The natural history of Mexican rattlesnakes.
University of Kansas Museum of Natural History Special Publications. (5):1-88.
Baird, S.F. 1859. Crotalus tigris Kennicott. Report on the United States and Mexican
Boundary Survey. 2:14.
Beaupre, S.J. 1995. Comparative ecology of the rock rattlesnake, Crotalus lepidus, in
Big Bend National Park. Herpetologica. 51:45-56.
Beaupre, S.J., and D.J. Duvall. 1998. Integrative biology of rattlesnakes: contributions
to biology and evolution. Bioscience. 48:531-538.
Beck, D.D. 1995. Ecology and energetics of three sympatric rattlesnake species in the
Sonoran Desert. Journal of Herpetology. 29:211-223.
Tiger Rattlesnake Ecology and Management – Goode & Wall 55
Campbell, J.A., and W.L. Lamar. 1989. The Venomous Reptiles of Latin America.
Cornell University Press, Ithaca, New York.
Duvall, D., S.J. Arnold, and G.W. Schuett. 1992. Pitviper mating systems: ecological
potential, sexual selection, and microevolution. In, Biology of the Pitvipers. Eds. J.A.
Campbell and E.D. Brodie, Jr. Selva, Tyler, Texas.
Duvall, D., J.K. OíLeile, S.G. Heald, and S.J. Beaupre. 1995. Urban rattlesnake status
and ecology. Final report to Arizona Game and Fish Department (U93032), Phoenix.
Ernst, C.H. 1992. Venomous reptiles of North America. Smithsonian Institution Press,
Washington. 236.
Fowlie, J.A. 1965. The snakes of Arizona. Azul Quinta Press, Fallbrook, California.
Gloyd, H.K. 1937. A herpetological consideration of faunal areas in southern Arizona.
Bulletin of the Chicago Academy of Sciences. 5:131.
Gloyd, H.K. 1940. The rattlesnakes, genera Sistrurus and Crotalus. Chicago Academy
of Sciences Special Publications. 4:1-266.
Goldberg, S.R. 1999. Reproduction in the tiger rattlesnake, Crotalus tigris (Serpentes:
Viperidae). Texas Journal of Science. 51:31-36.
Klauber, L.M. 1931. Crotalus tigris and Crotalus enyo, two little known rattlesnakes of
the southwest. Transactions of the San Diego Society of Natural History. 4:353-370.
Klauber, L.M. 1935. Notes on herpetological collecting. San Diego Natural History
Society. Collecting Leaflet No. 1.
Klauber, L.M. 1956. Rattlesnakes: their habits, life histories and influence on mankind.
1st Edition. University of California Press, Berkeley, California.
Klauber, L.M. 1972. Rattlesnakes: their habits, life histories and influence on mankind.
2nd Edition. University of California Press, Berkeley, California.
Lowe, C.H., C.R. Schwalbe, and T.B. Johnson. 1986. The venomous reptiles of Arizona.
Arizona Game and Fish Department, Phoenix, Arizona.
McNally, J, and T. Hare. 1996. Evaluation of a rattlesnake relocation program. Final
report submitted to the Arizona Game and Fish Department (U93009), Phoenix.
Tiger Rattlesnake Ecology and Management – Goode & Wall 56
Nowak, E.M., and C. van Riper, III. 1999. Effects and effectiveness of rattlesnake
relocation at Montezuma Castle National Monument. Technical Report
#USGSFRESC/COPL/1999/17. USGS Forest and Rangeland Ecosystem Science Center,
Biological Resources Division, Colorado Plateau Field Station. Northern Arizona
University. Flagstaff, Arizona.
Prival, D.B., M.J. Goode, D.E. Swann, and C.R. Schwalbe, M.J. Schroff, and R.J. Steidl.
1999. A comparative study of hunted vs. unhunted populations of the twin-spotted
rattlesnake. Final report to Arizona Game and Fish Department, Phoenix.
Prival, D. B., and C. R. Schawalbe. 2000. Conservation and management of
commercially valuable snake species at Chiricahua National Monument. Final report to
the Southwestern Parks and Monuments Association.
Reinert, H. K., and D. Cundall. 1982. An improved surgical implantation method for
radio-tracking snakes. Copeia. 3:702-705.
Reinert, H.K., and R.R. Rupert. 1999. Impacts of translocation on behavior and survival
of timber rattlesnakes, Crotalus horridus. Journal of Herpetology. 33:45-61.
Rocking K Specific Plan. 1991. Pima County, Arizona.
Rocking K Specific Plan (Amended). 1996. Pima County, Arizona.
Rubio, M. 1998. Rattlesnake: portrait of a predator. Smithsonian Institution Press,
Washington and London.
Schuett, G.W., and J.C. Gillingham. 1988. Courtship and mating of the copperhead,
Agkistrodon contortrix. Copeia. 1986:807-811.
Schuett, G.W. 1992. Is long-term sperm storage an important component of the
reproductive biology of temperate pitvipers? In, Biology of the Pitvipers. Eds. J.A.
Shine, R. 1978. Sexual size dimorphism and male combat in snakes. Oecologia.
33:269-277.
Turner, R. M., and D. E. Brown. 1982. Sonoran desertscrub vegetation. Desert-Plants.
4:181-219.
Wright, A.H., and A.A. Wright. 1957. Handbook of snakes of the United States and
Canada. Comstock Publishing Company, Ithaca, New York.
Tiger Rattlesnake Ecology and Management – Goode & Wall 57
APPENDIX A
Raw data from 169 tiger rattlesnakes captured at three sites in and adjacent to Saguaro
National Park, and by Rural Metro Fire Department personnel in the foothills of the Santa
Catalina Mountains. LR = Loop Road, TVR = Tanque Verde Ridge, A = adult, Repro =
reproductive status, NG = not gravid, G = gravid, NS = no semen present, S = semen
present, SVL = snout-vent length, TL = tail length, HW = head width, HL = head length,
RS = number of rattle segments, RL = rattle length, RB = rattle broken, Y = yes, and N =
no. All measurements are in millimeters except mass, which is in grams.
1997
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
08/04/97 LR F A NG 670 51 175 17 26 9 44 Y
08/06/97 LR F A G 521 29 175 21 19 4 24 N
08/07/97 TVR F A NG 592 43 259 20 26 8 40 Y
08/10/97 LR M A NS 709 74 471 23 34 10 51 Y
08/12/97 TVR M A NS 680 73 283 20 29 7 36 Y
08/12/97 TVR M A NS 667 64 292 21 29 6 33 Y
08/13/97 TVR M A NS 778 71 380 7 35 Y
08/17/97 LR M A S 713 73 369 23 30 7 18 Y
08/26/97 TVR F A NG 636 45 186 21 28 8 35 Y
08/26/97 LR M A NS 635 72 316 20 29 8 38 Y
08/26/97 LR M A NS 712 46 214 22 30 8 29 Y
08/26/97 LR M A S 656 66 346 28 7 29 Y
08/26/97 LR M A S 673 69 310 31 8 38 Y
08/27/97 TVR F A NG 637 45 261 21 25 7 29 Y
08/27/97 TVR F A NG 600 46 291 21 30 7 30 Y
08/27/97 LR M A NS 730 73 337 22 32 10 49 Y
08/27/97 TVR M A S 650 65 261 20 31 5 27 Y
09/02/97 TVR F A NG 688 47 226 20 27 8 33 Y
09/05/97 TVR M A S 680 66 325 20 31 9 43 Y
09/12/97 TVR F A NG 627 45 251 18 26 7 38 N
09/27/97 TVR M A NS 694 65 317 19 29 9 Y
10/02/97 TVR M A S 687 71 355 26 28 7 32 Y
10/15/97 TVR M A NS 647 58 236 22 29 6 30 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 58
1998
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
05/23/98 TVR M A NS 694 63 348 21 29 7 32 Y
07/03/98 TVR F A NG 647 43 275 19 27 8 35 Y
07/08/98 TVR M A NS 612 43 263 26 17 9 43 Y
07/17/98 LR M A NS 741 72 357 21 30 9 40 Y
08/02/98 LR F A NG 659 50 231 19 27 10 45 Y
08/02/98 LR M A S 728 67 356 18 28 9 41 Y
08/02/98 LR M A S 629 56 257 20 26 7 Y
08/09/98 RK M A S 699 70 388 22 29 10 49 Y
08/10/98 LR M A NS 687 74 400 23 26 9 44 Y
08/12/98 TVR M A S 627 58 299 22 27 8 32 Y
08/12/98 LR M A S 732 65 496 23 28 6 30 Y
08/12/98 TVR M A NS 738 67 433 22 28 9 49 Y
08/12/98 TVR M A S 693 68 401 22 29 7 44 Y
08/20/98 LR M A S 697 63 357 23 30 12 51 Y
08/20/98 LR M A S 602 60 260 21 27 7 35 N
08/21/98 TVR M A NS 553 51 185 19 25 6 31 N
08/23/98 LR M A S 772 69 512 21 29 10 43 Y
08/25/98 TVR F A NG 650 51 264 20 27 9 40 Y
08/27/98 LR F A G 610 42 236 21 30 10 43 Y
08/27/98 LR M A NS 602 67 395 22 30 7 35 Y
08/30/98 TVR F A NG 635 45 243 20 29 8 34 Y
08/31/98 TVR F A NG 658 42 326 19 28 10 45 Y
09/02/98 LR M A S 636 66 291 20 26 7 31 Y
09/04/98 RMFD M A S 730 70 474 23 28 6 34 Y
09/04/98 RMFD F N NG 252 18 18 13 17 1
09/11/98 TVR F A NG 564 35 158 17 24 3 20 Y
09/12/98 LR M A S 725 65 390 19 28 10 49 Y
09/21/98 LR M A S 729 71 400 18 28 10 50 Y
10/21/98 RMFD M A S 659 56 281 19 25 10 46 Y
10/21/98 RMFD F A 577 46 239 19 23 7 40 N
10/21/98 RMFD F A G 669 46 369 20 25 10 31 Y
10/24/98 TVR M A NS 601 55 215 19 23 7 36 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 59
1999
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
05/27/99 TVR M A 682 60 285 19 27 8 38
05/01/99 LR F A G 597 43 362 6 Y
06/30/99 RMFD M A 700 64 360 33
07/03/99 RMFD M A 713 67 384 43 Y
07/26/99 RK M A NS 682 66 305 21 27 9 45 Y
07/30/99 RK F A NG 634 50 148 16 25 8 30 Y
08/04/99 TVR F A NG 537 41 156 17 22 5 25 N
07/28/99 RMFD M A S 767 73 469 24 30 4 25 Y
07/26/99 RMFD F A 511 41 156 18 23 5 24 N
07/26/99 RMFD F A 534 39 160 19 24 5 24 N
08/02/99 RMFD F A NG 584 36 278 18 27 8 33 Y
08/02/99 RMFD M A S 535 58 161 18 25 5 23 N
07/15/99 RMFD M A S 636 55 165 17 25 5 24 N
08/31/99 RK M A S 684 66 288 20 28 11 50 Y
08/30/99 TVR F J NG 511 38 113 17 25 5 25 N
09/01/99 TVR M A S 712 66 345 21 31 10 50 Y
09/02/99 RK M A S 739 71 385 21 30 10 51 Y
09/04/99 RK M A NS 636 74 378 22 29 9 46 Y
09/05/99 RK M A NS 761 70 426 24 31 10 46 Y
09/05/99 RK M A S 638 59 246 19 27 5 27 Y
09/05/99 RK F A NG 596 41 179 19 26 7 32 Y
09/05/99 RK M A NS 686 68 234 22 29 6 30 Y
09/06/99 RK M A S 753 69 415 24 33 10 49 Y
09/14/99 RK F A NG 619 36 150 16 25 6 27 Y
09/14/99 TVR M A S 711 64 455 26 29 8 39 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 60
2000
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
06/05/00 RK M J NS 394 34 46 15 22 1 14 N
06/05/00 RK M J NS 561 52 134 22 27 5 Y
06/13/00 LR M A 692 68 340 21 28 12 49 Y
06/27/00 RK M A NS 649 64 265 20 26 9 40 Y
06/29/00 RK M J 357 37 53 14 20 3 18 Y
06/29/00 LR M A 531 44 158 17 24 5 25 N
07/01/00 TVR F A NG 681 51 249 22 29 10 40 Y
07/02/00 TVR M A NS 632 55 195 17 25 6 27 Y
07/05/00 RK M A NS 689 67 308 21 30 10 48 Y
07/10/00 RK M A NS 712 63 298 20 29 9 39 Y
07/11/00 RK F A NG 667 48 252 21 28 9 42 Y
07/11/00 RK M A NS 716 62 383 21 30 9 46 Y
07/11/00 RK M A S 658 59 301 22 29 10 51 Y
07/13/00 RK M J S 492 48 95 18 24 5 24 Y
07/14/00 LR M A S 737 73 434 23 29 7 35 Y
07/14/00 LR F J NG 477 35 102 20 25 4 19 N
07/14/00 LR M A NS 699 67 336 21 29 10 44 Y
07/15/00 LR M A S 676 63 297 21 29 9 41 N
07/15/00 LR M A NS 749 62 315 23 30 10 43 Y
07/17/00 RK F A NG 569 39 183 19 26 6 29 N
07/17/00 RK F A NG 614 44 141 19 26 6 20 Y
07/17/00 RK M A NS 661 64 275 21 28 21 28 Y
07/17/00 RK M N NS 283 24 20 14 18 1 8.1 N
07/19/00 RK F N NG 286 21 19 13 18 1 9 N
07/20/00 TVR F A NG 624 42 266 24 28 11 47 Y
07/22/00 RK M A S 690 65 284 20 27 8 36 Y
07/24/00 RK F A NG 669 46 196 21 28 5 26 Y
07/24/00 RK M A NS 610 63 227 10 42 Y
07/24/00 RK M A S 684 61 332 19 29 9 37 Y
07/25/00 RK F A G 630 40 208 23 30 10 45 Y
07/25/00 RK F A G 539 38 154 19 25 6 30 N
07/27/00 RK M A S 704 70 418 25 31 9 46 Y
07/27/00 RK M A S 739 65 320 23 28 13 56
07/28/00 RK F A NG 683 44 183 21 28 9 42 Y
07/28/00 RK M A NS 639 62 260 23 29 8 34
08/01/00 RK M A S 542 51 147 19 25 3 18 Y
08/08/00 TVR M A S 653 57 270 21 28 7 34 Y
08/10/00 RK F A NS 541 41 182 18 24 6 26 N
08/10/00 RK F N NG 294 25 20.5 13 19 1 8.7 N
08/12/00 TVR M A S 562 53 142 25 27 6 30 N
09/02/00 RK M A S 560 59 145 19 24 6 29 N
Tiger Rattlesnake Ecology and Management – Goode & Wall 61
2000 (con’t.)
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
09/09/00 RK M A S 605 58 209 18 26 6 31 N
09/20/00 RK M J S 448 39 73 16 23 4 20 N
09/20/00 RK F J NG 426 35 60 14 20 4 19 N
09/25/00 RK M J S 580 56 129 17 25 5 27 N
09/28/00 TVR M A S 742 68 354 21 28 11 42 Y
09/30/00 RK M A S 590 58 154 18 26 8 33 Y
10/01/00 RK M A S 676 68 345 21 29 9 46 Y
10/25/00 RMFD M A S 666 68 398 23 29 8 37 Y
11/10/00 TVR M A NS 538 49 114 16 24 5 24 N
2001
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
04/28/01 RK F J NG 180 29 31 18 17 1 9 N
05/24/01 RK F J NG 550 38 140 18 25 8 41 N
05/27/01 RK F J NG 356 26 47 17 20 2 12 N
06/10/01 LR M J NS 544 49 176 22 26 6 29 N
06/17/01 RK F J NG 511 34 95 18 23 5 27 N
06/18/01 RK M J NS 327 27 24 14 18 2 13 N
07/04/01 TVR M A S 554 56 146 17 26 6 28 N
07/09/01 LR F A G 646 44 278 23 28 10 42 Y
07/09/01 LR M A NS 618 68 237 19 26 6 25 Y
07/11/01 RK M A NS 731 70 421 25 31 9 43 Y
07/11/01 RK M J NS 645 51 164 19 25 5 25 N
07/13/01 RK M A NS 553 55 180 21 27 5 24 Y
07/15/01 LR F A G 599 41 225 20 28 6 31 Y
07/16/01 LR M A NS 772 68 436 21 29 3 15 Y
07/16/01 RMFD M A NS 607 52 177 18 25 7 33 Y
07/16/01 RMFD M A NS 651 60 215 20 28 7 32 Y
07/23/01 LR M A NS 607 57 196 17 26 7 34 N
07/23/01 LR F A NG 599 40 219 18 26 7 36 N
07/24/01 LR M A NS 696 64 313 19 28 7 35 Y
07/30/01 RK M A S 646 66 247 22 28 9 42 Y
07/30/01 RK F A G 554 39 167 19 23 7 32 Y
08/04/01 RMFD M A NS 716 65 354 22 30 5 23 Y
08/05/01 RMFD M A NS 733 65 491 22 27 11 55 Y
08/06/01 RK M A NS 689 64 285 18 27 10 47 Y
08/06/01 RK M A NS 703 69 383 22 26 8 38 Y
08/08/01 RK M J S 496 43 86 19 22 4 22 Y
Tiger Rattlesnake Ecology and Management – Goode & Wall 62
2001 (con’t.)
Date Site Sex Age Repro SVL TL Mass HW HL RS RL RB
08/09/01 RK M A NS 690 62 323 20 28 12 50 Y
08/09/01 LR M A NS 689 67 306 20 29 6 30 Y
08/13/01 RK M A NS 670 62 287 21 27 6 27 Y
08/13/01 RMFD M A S 637 54 259 19 28 6 33 N
08/14/01 RMFD M A NS 708 68 389 21 28 3 19 Y
08/16/01 RK M J NS 545 59 157 17 25 7 33 Y
08/25/01 RK M A S 578 54 184 18 25 7 28 Y
08/30/01 RMFD M A Y
09/07/01 RK M J S 502 52 129 17 21 5 24 N
09/08/01 RMFD M A S 707 66 22 29 8 32 Y
09/23/01 RK F A G 546 37 190 17 26 6 29 N
09/22/01 LR F A NG 578 45 228 19 28 7 29 Y